A crucial eligibility criterion for this systematic review is the reporting language. All the resources necessary for this review were supposed to have been reported in English. All articles and other resources reported in other languages were excluded from this systematic review irrespective of their usefulness.

The studies to be included in this systematic review had to present information contributing to socio-moral development. Research studies using quantitative methods compatible with theoretical approaches were considered eligible for inclusion in the systematic review. Any other studies contrary to the above information were automatically removed from the inclusion list.

All the studies that reported positive moral development as an outcome measure were added to the inclusion list for the systematic review. Studies and resources that were not aimed at reporting on this particular outcome measure were automatically excluded from this systematic review.

A total of 602 studies were retrieved electronically from the search databases, Cross-reference, Google Scholar and PubMed. In the preliminary screening, all 602 articles were used, and then, 433 articles were removed as duplicates. Furthermore, 131 studies were eliminated based on invalid abstracts and titles. Till this stage, 48 studies survived the elimination process. All 48 articles were tested on the eligibility criteria, and 22 articles were eliminated after a complete text analysis was done. The remaining 26 studies were consistent with the inclusion demands and were, therefore, considered for the systematic review. Figure 1 presents the PRISMA model utilised for the search strategy in this systematic review. Table 1 below shows the main information of the papers.

The research problem of whether moral sense is wholly socialised or natural has, to date, not been settled despite the numerous studies conducted on this problem. However, quite a few studies have shown that infants and young children exhibit different moral skills at a young age. One-year-old children are seen to explore their social environment by employing inherent skills. According to Carpendale and Hammond (2016), children always help their parents in their daily activities. They are seen to actively take part in fulfilling daily obligations without necessarily being instructed to do so. This shows that young children possess natural moral abilities to decide what is good and what is not. They distinguish between the virtue of helping parents and the wickedness of staying idle. Other researchers have also interpreted that morality emerges naturally in humans (Carpendale and Hammond, 2016). Moral sense is naturally present in a human being, irrespective of their age. Infants and young children possess natural morality that allows them to distinguish between the simple definitions of proper and improper.

A study to assess the moral judgements of young children was also conducted to establish how children view moral transgressions (Smetana and Ball, 2018). In this study, young children aged between 4 and 9 years were tested to determine their response to physical harm, resource transgressions and psychological harm to their enemies and friends. Among the children, transgressions against their enemies were more accepted than those against their close friends. Moreover, the transgressions were least intended when targeted at close friends compared to enemies. Smetana and Ball (2018) confirmed that children considered moral transgressions as improper and wrong. This establishes that the children, across all relationships, distinguish between right and wrong or good and bad. Thus, moral sense is considered to be natural.

Smetana and Ball (2019) conducted another study to ascertain whether age is a determining factor in children developing their moral judgements concerning different types of harm. This study concentrated on children aged 4–9 years and sought to determine their moral judgements from age profiles based on different types of harm. Ultimately, the authors found that children of different ages portrayed significant differences in moral understandings regarding other forms of harm (Smetana and Ball, 2019).

Young children, aged four, depicted little moral understanding of different types of harm. On the other hand, grown-up children, aged nine, had a greater moral understanding of these. In general terms, Smetana and Ball (2019) confirm that children’s moral judgement is organising according to their ages. Young children made weak moral judgements, whereas older children made strong moral judgements. This shows that children’s moral judgements develop naturally with respect to their ages. 160 children aged 4–9 were observed to evaluate the emotions, judgements, intentions and justifications they manifested with respect to physical and psychological damage and transgressions aimed at acquaintances, friends, disliked peers and bullies. Transgressions against bullies were found to be more acceptable among the children than those against friends and disliked peers and were deemed to be less deserving of punishment. In addition, the children viewed moral transgressions as wrong based on the principles of well-being and fairness.

Geraci and Simion (2021) investigated whether the perception of the social-causal relationship triggers both children’s evaluation processes and expectations relating to the social preferences of third parties. To this end, three experiments were implemented that reproduced a social causality, a physical causality and a choice task to assess children’s preferences.

Research results (Geraci and Simion, 2021) have demonstrated that children’s evaluations are triggered by their perception of social causality: Only in a social condition did children expect a spectator to help an intermediary agent. Explain the children’s actions and their relationships with each other and with adults, and then, evaluate these actions. Korotaeva and Chugaeva (2019) focus on the study of the moral representations of preschool children. This experiment was conducted among preschool children in one of the groups of the Ekaterinburg kindergarten. The theoretical basis of reference was that social behaviour is characterized by duality: on the one hand, a person’s actions are determined by social standards and norms; on the other hand, the actions are controlled by the person and his/her ability to choose and take responsibility for that choice. During childhood, a child experiences social relationships, learns to solve problems and assimilates moral standards through personal perception. The experimental study demonstrates the importance of developing methodical recommendations for interactions between teachers and children, or between parents and children, to mediate effective social and moral education that takes into account the children’s perspectives on moral standards and rules of conduct. Thus, the authors highlight the importance of adults in the development of moral sensibility by respecting the personal ideas of the children. Franchin et al. (2019) suggest that children within 30 months begin to associate goodness with socio-moral characteristics such as a helping disposition but do not do so regarding equity in distributive actions. The ability to distinguish between intentions and outcomes in morally relevant events is present at the age of 8 months (Hamlin, 2013a). The “moral mind” of the young child is fundamentally different from that of older children and adults. However, as early as 8 months, children incorporate, and even prioritize, intentions in their social assessments. Instead, 5-month-olds appear to be able to distinguish only the characters who intend the outcomes they cause.

Hamlin (2013b) also argues that human morality is a fundamental and innate aspect of human nature, as it supports cooperation. This mental function has developed with the evolution of the human being who needed to aggregate to survive. Hamlin demonstrates that infants naturally engage in surprisingly sophisticated and flexible behaviour and moral assessments.

A section of these studies concerns how individuals can naturally respond morally to various dilemmas: Geraci and Franchin (2021) investigated whether 21-month-olds expect non-needy agents to help agents in need (type of puppet) of food or shelter. The results show that when agents in need are morphologically similar to agents in need, children watched the event longer, which showed that agents in need help agents in need. Fourteen-month-old babies were familiarised with a character who helped or hindered another agent’s attempts to reach the top of a hill. The hinderer condition started with the same familiarization phase used in the helper condition, but in the test phase, the distributor of the strawberries was the hinderer instead. The preliminary analysis assessed the effects of the order of familiarization events (Help, Hinder, Hinder, Help vs Hinder, Help, Help, Hinder) and the identity of the helper and the hinderer (Square vs Triangle). It found that they had no main effect on looking times at the test trials, nor was there a significant interaction between such factors and the type of test event (equal vs unequal distribution). Children who saw the helper perform an unequal distribution looked longer than those who saw the helper perform an equal distribution, while the children who saw the hinderer perform an unequal distribution looked the same way as those who had seen the hinderer perform an equal distribution (Surian et al., 2018). Lavoie et al. (2021) confirm the findings of previous studies through a review centred on the methods used to measure the moral development of children under the age of two. They show that moral sense is innate, that is present from birth.

As mentioned earlier in this paper, people’s moral sense develops over time due to social interactions. In this context, children are considered to encounter moral development when they interact with their parents or even peers. According to various studies, the issue of the emergence of the moral sense has continued to be unclear, and whether moral development is wholly socialised or naturally acquired is a topic of debate still yet. Nonetheless, studies have found that the uniqueness of interactions significantly contributes to moral development. In a social context, moral knowledge is enhanced when a person is exposed to others’ views and ideas. An individual can grow and develop morally only if the social interactions experienced are educative. In general terms, the active discussions and negotiations a person participates in are the pillars of moral development.

Govrin (2014) produced a general model of the process that contributes to the development of moral judgement in the first year of life, whereby a universal and innate structure of the moral faculty is hypothesised, which is therefore pre-reflexive. However, the latter develops through early interactions with the caregiver. The internal representations that the child constructs in the dynamic system with the caregiver determine their judgements about what is wrong and what is right. This work suggests explaining the mind in the first year of life by integrating Bowlby’s attachment theory, ethics of care and moral psychology that were previously regarded as separate domains.

Another literature review was conducted by Carpendale and Hammond (2016) to pinpoint the source of moral norms among children and infants. The authors sought to examine previous claims that proposed that infants have a natural moral understanding. While examining this information, the study aimed to establish the source of the children’s moral knowledge—whether it occurred naturally or was socially nurtured. In the review, Carpendale and Hammond (2016) categorically presented the views of the previous researchers. According to them, previous studies stated that children help their parents – young children are always seen to take part in daily activities. Moreover, they put forward that children are interested in pleasing people but are scared away by bad people. This has been interpreted as human beings possessing natural morality.

However, the aforementioned explanation from Carpendale’s review has given rise to more questions than solutions. As in the above case, the source of morality is still unclear – whether it is wholly socialised or natural.

Geraci et al. (2021) evaluated the reactions of preschool children in different situations of social interaction. They show that children preferred the character who consoled the victim over the one who did not. Thus, it emerges that social assessments are based exclusively on social interactions between prosocial/antisocial agents and recipients. Furthermore, the authors’ findings reveal an evolutionary tendency in children to reward the puppet who comforts and punish the puppet who ignores the victim.

Carpendale and Hammonds’ study Carpendale and Hammonds’ (2016) also concentrated on examining the source of this moral sense. The daily interaction between children and caregivers is seen to significantly foster children’s ability to coordinate morally with others (Cingel and Krcmar, 2020). Through social interactions between them and their superiors, children are able to equip themselves with sufficient moral skills and ultimately nurture their inbuilt moral senses. The authors conclude that children’s moral development is significantly boosted by the continuous daily interactions they have with parents and guardians. Thus, according to Carpendale and Hammond (2016), moral development is socialised, that is social interactions contribute to morality enhancement.

Mammen et al. (2019), in their research study, focused on how children develop their moral judgements through socially interacting with their parents and peers. This study sought to investigate the differences in talking about moral problems when children interact with their parents and their peers. With their parents, the interaction is seen to contribute little as far as the moral development of the children is concerned (Mammen et al., 2019). Children are depicted in Mammen’s study as lacking enough freedom to talk about their parents’ problems. Mothers and other adults do not always negotiate or discuss moral challenges with their children. This, therefore, denies children the opportunity to develop moral skills for tackling different moral issues.

Conversely, children are seen to negotiate and discuss their dilemmas with their peers freely. They believe that with their peers, who are of an equal level, moral problems can be actively discussed. This, therefore, enhances their experience and, in turn, develops their moral senses. Based on these perspectives, social interactions, especially with peers of an equal level, give individuals the best opportunity to negotiate their moral challenges. This develops them morally, hence contributing to their moral sense. Studies (Chiasson et al., 2017) have focused on changing socio-moral reasoning from infancy to adolescence, and results show that boys with conduct disorders tend to differ from their healthy counterparts in terms of their level of socio-moral maturity of judgement. The factors of “intelligence” and “maternal support” are known to exert a decisive influence on the level of socio-moral development (Baker et al., 2022). The main goal of Hammond et al. (2021) was to show the results of an educational programme on self-control and moral development taught to a sample of abused and abandoned adolescents. Another aim of this subject concerns socio-moral development from the point of view of social representations (Emler, 2021). Significant interpersonal relationships make it possible to construct representations of oneself, of the Other and of the World by mediating cognitive schemes that filter the interpretations and evaluations of one’s own and others’ actions. This process structures the moral sense in the child who develops and matures in the first years of life.

Goffin et al. (2020) experimentally demonstrated the positive association between the mind-mindedness of the mother and that of her children and the theory of mind of the children. Finally, Dahl (2019) examined research on how children’s orientations towards helping and harming others gradually develop through daily social interactions in their early years.

Concerns for the welfare of others, rights, equity, and justice serve as the foundation for structuring the moral sense for the judgement of what is right and wrong. The authors affirm that this passage from a primary to a complex moral is allowed by daily interactions. Therefore, morality is neither innate nor solely the result of caregiver relationships.

The environment plays a significant role in shaping the moral sense of human beings. Behavioural expectations are made clear to children when the physical environment is set appropriately. The physical environment provides young children with expectations of behaviour. When educators are aware of the aesthetics, organization, and function of each area of the space, defiant behaviour is likely to decrease while constructive and cooperative behaviour increases. A well-designed curriculum provides the best opportunity for children to access a wide range of items and ideas that reflect their interests. This great accessibility allows young children to freely discuss their interests with each other. The environment’s design is crucial as far as moral development is concerned (Paris et al., 2021). For young children, a space of tremendous and well-designed learning is constructive and interactive. Such an environment has learning materials placed at a location readily accessible to individuals, and children can freely utilise the materials based on their interests. They can negotiate with each other over the materials they have. Additionally, ample space enables child–adult interactions. This creates an opportunity to expand interactions and discussions. The expansion of discussion and negotiation boosts the moral abilities of the people involved in the conversation.

A well-designed physical environment is always observed to be socially attractive. According to Paris et al. (2021), a learning environment designed with quality in mind sets the best background for boosting socio-emotional development. The preparation of a high-quality environment with sufficient learning items is attractive to children and adults. This attraction allows the concerned individuals to participate in activities of their interests and abilities fully. This, in turn, further develops their moral senses. An environment that enables moral development comprises ample and diversified learning space, enough supply of material, supportive engagements and displays of individuals’ work.

A socially attractive environment must possess a number of user-friendly factors, such as ample interaction space, and it should be well equipped with the necessary resources. An individual exposed to this space is free to make moral judgements based on the available resources. Notably, a person plays with the environmental resources based on their interest and ability. This contributes to moral development through enabling constructive interactions and engagements. As stated, it allows individuals to freely explore their interests and abilities by utilising the ample resources available to them. Therefore, young children are allowed to manage their relationships and themselves fully. Through this, they are able to develop morally. Environmental factors, consequently, enable moral development.

The social environment is a precursor to morality and moral development (Cowell and Decety, 2015). A study conducted by Cowell and Decety (2015) found that socio-environmental factors support the sensitivity of moral sense among toddlers and young infants. As confirmed by Cowell and Decety (2015), the minds of young children are biologically prepared. They are already in possession of moral sense. Human beings are biologically predisposed to the construction of moral judgements and evaluations, which, therefore, structure behaviours aimed at cooperation and associations between antisocial actions and punishments. The interaction between the environmental factors and these infants’ minds impacts their behaviour and social evaluation (Cowell and Decety, 2015).

This is the result of their study that looked at the neural basis and precursors of moral sensitivity in 73 subjects aged 12–24 months. The analyzes performed were of electrophysiological, eye-tracking, behavioural and socio-environmental nature. The study established the interaction of prepared minds with supportive environmental factors to be a great contributor to socio-moral development. The social and moral behaviours of the involved individuals develop when exposed to various environmental foundations. In other words, a person exposed to various supportive factors is well-positioned to behave differently from their previous behaviour; this is moral development. Considering the above perspectives, environmental factors contribute significantly to moral development. Two specific areas are evaluated in the study by Holvoet et al. (2016): (1) studies that have previously explored social assessment skills beyond a basic preference for prosocial behaviour and (2) current theories attempting to explain how and why such preferences could exist so early in childhood. Ting and Baillargeon (2021) explore how young children value other characters on a moral level and reveal how these ratings, in turn, allow children to form sophisticated expectations about the behaviour of others in new contexts. Denton and Krebs (2017) examine the psychological and neurological evidence supporting dual moral decision-making models and discuss research that has attempted to identify triggers for rational-reflexive and emotional-intuitive processes. Dahl and Baxley (2016), on the other hand, present the main theoretical perspectives on the early development of morality and its basic elements during the first 4 years of life. Finally, research on infants and young children suggests that even during early development, humans evaluate others by considering the outcome of an action in relation to the intention behind it. On this note, Hilton and Kuhlmeier (2019) review existing research on moral evaluation and propose that differences in how intentions and outcomes of behaviours are viewed may (1) support or preclude attribution of intentions to young children and (2) alter the relative relevance or predominance of any type of information.

In conclusion, the studies that can be categorized in the socio-environmental approach consider the environmental and social factors determining moral development, but they also agree on the existence of a predisposition to prosociality present from birth.

This systematic review included 26 studies. Although these studies used different methodological approaches, all of them contributed to the topic under study. Neverthless, the emergence and development of moral sense is a theme that still requires further study, as studies focusing on this area are few and far between. The facts and research available claim that moral sense is naturally occurring (Garrigan et al., 2018). Infact, many researchers have found it difficult to determine the source of morality in humans – whether moral sense is wholly socialised or natural. This stand is also consistent with Kotlova (2020) findings that children view moral transgressions as being wrong. These interpretations thus converge, indicating that morality and moral judgements are innate across all social relationships.

Morality may be taught and developed even though it is innate (Cowell and Decety, 2015). Social relationships create a suitable environment for individuals to share, discuss and negotiate their dilemmas with ease. Thus, social interactions equip individuals with ample space to shape their moral skills (Lapsley et al., 2022). People exposed to a wide range of constructive social interactions can better negotiate their problems than individuals exposed to less constructive interactions. According to Mammen et al. (2019), the interaction between a child and a coequal peer is more productive than an interaction between a child and a parent. A child discusses their moral problems more with a peer than with a parent. Based on this, moral development is enabled by child–peer interactions more than child–parent interactions.

Moral development is not fostered by social interactions only; it can also be encouraged by exposing minds to various constructive and interactive environmental factors (Malle, 2021). Children’s learning environments are seen to promote moral development the best. Quality learning environments set the stage for exploration and socio-emotional growth. When children are presented with a warm, welcoming, culturally motivating and familiar environment, they feel comfortable and safe. The attractive spaces that adults prepare for children communicate expectations of responsibility and cooperative union (Hamlin, 2013a).

A well-designed environmental space with ample resources is considered fit for moral development. In such spaces, children can freely utilise the resources available to make judgements based on their interests (Paris et al., 2021). These environments have various characteristics: challenging and developmentally appropriate materials, ample supply of materials, appropriately sized small-group activities, a variety of small-group activities within a range of adult supervision, aesthetically appealing spaces to be with others and spaces to be alone, furnishings and materials accessible to children, displays of children’s work and support for children’s active engagement.

Additionally, the ample space provided by such an environment allows the concerned individuals to interact freely. The interaction between a child and an adult also gives rise to good opportunities for resolving moral dilemmas; this is done by posing questions and discussing them.

The three areas in which the selected studies have been categorized are: “Natural Moral Sense,” “Social Relationships and Moral Development,” and “Environmental Factors and Moral Development.” Although each approach proposes a different aetiology of the moral sense, the review brings out an agreement among the authors regarding the presence of a predisposition to morally acceptable behaviours (Cowell and Decety, 2015; Dahl, 2019; Korotaeva and Chugaeva, 2019) that mature and are influenced by life experiences determined by interpersonal relationships and environmental factors.

In general, this systematic review summarises the findings from various research studies and articles and provides a definite conclusion. First, moral sense is innate. Second, moral development is considerably strengthened through social interactions and exposure to constructive and interactive environmental factors.

The number of studies included in this systematic review was small. This can be mainly attributed to the strict criteria used during the inclusion and exclusion process. To establish a consensus on a specific area of study, numerous articles need to be included. Therefore, the small number of the studies analysed in this systematic review limits the accuracy of the conclusion reached. Limited data available for a systematic review is considered to limit the consensus achieved.

Furthermore, only items reported in English and those meeting the required study characteristics were considered relevant for this systematic review. Items that were reported in languages other than English, irrespective of their usefulness, were declared irrelevant for this systematic review. The use of articles published in a single language is a source of bias. Research studies reported in other languages are never promoted.