Children are one of the most important agencies of waste separation. They are also potential future leaders and can bring robust social impacts to people around them (Meinhold and Malkus, 2005; Liao and Li, 2019; Deng et al., 2022; Wang et al., 2022). Moreover, children’s environmental attitude and behavior today can directly affect their future attitude and behavior (Evans et al., 2007; Arı and Yılmaz, 2017; Otto et al., 2019). Therefore, it is necessary to develop tailored promoting strategies for children. Accordingly, it is essential to explore the determinants of children’s waste separation behavior, and find these aged-related differences between children and adults.

Many studies have explored the factors influencing adults’ waste separation behavior. For instance, attitude (Wang, 2021), perceived behavioral control (Shi et al., 2021; Wang et al., 2021; Lou et al., 2022), intention (Shi et al., 2021; Wang, 2021), contextual factors (Fan et al., 2019; Meng, 2019; Leeabai et al., 2021), habitual factors (Fan et al., 2019), knowledge (Meng, 2019), and incentive measures (Wang et al., 2020) play positive roles in waste separation behavior. However, there is relatively little research on children’s waste separation behavior.

Prior studies on primary students’ environmental behavior mainly focus on general environmental behavior (Evans et al., 2007; Chawla and Derr, 2012; Collado et al., 2015; Otto and Pensini, 2017), sustainable behavior (Tucker and Izadpanahi, 2017; Ebersbach and Brandenburger, 2020), recycling behavior (Kumar, 2019; Šorytė and Pakalniškienė, 2021), and food waste (Niaki et al., 2017; Sorokowska et al., 2020), but neglect waste separation behavior. What are the main factors influencing children’s waste separation behavior, and are these factors different from those for adults? To narrow the research gap, this study focused on children’s waste separation behavior and made a comparison with adults by using the theory of planned behavior (TPB; Ajzen, 1991).

TPB is one of the most influential models for exploring the factors affecting people’s behavior (Yuriev et al., 2020), and is widely used in research on environmental behavior (Yu et al., 2018; Meng, 2019). However, to our knowledge, applications of extended TPB to children’s waste separation behavior are scarce. Moreover, since TPB has some limitations due to its incompleteness (de Leeuw et al., 2015; Yuriev et al., 2020), researchers have expanded TPB by adding other factors to enhance its predictive power, such as knowledge (Pothitou et al., 2016; Liao and Li, 2019; Xie and Lu, 2022), social norms (Goh et al., 2022; Guo et al., 2022), descriptive norms (Qalati et al., 2022), moral norms (Wan et al., 2017), moral responsibility (Qalati et al., 2022), and awareness of the consequences (Wan et al., 2017; Kumar, 2019; Meng, 2019; Zhang et al., 2019). Knowledge is an important prerequisite for action (Otto and Pensini, 2017), and awareness is recognized as the important antecedent of behavior (Fu et al., 2020). Therefore, we integrate knowledge and awareness to TPB, and attempt to answer the two key questions: (1) Could children’s waste separation behavior be explained by the expanded model of TPB? (2) Is there any difference in the influencing factors between children’s and adults’ waste separation behavior?

The present study provides three main contributions. First, it tests the determinants of children’s waste separation behavior. Second, it explores the differences in waste separation between children and adults. Third, it extends TPB by adding two additional variables (i.e., knowledge and awareness) to better understand children’s and adults’ waste separation intention and habit formation processes.

The present study provides an expanded model of TPB to explore 9 to 12 years old children’s waste separation behavior, and makes a comparison between the key factors of children’s and adults’ waste separation behavior. Environmental behavior in childhood has a significant positive effect on individual’s such behavior in adulthood (Evans et al., 2007; Arı and Yılmaz, 2017; Otto et al., 2019), and can affect the environmental attitude and behavior of elders around them (Meinhold and Malkus, 2005; Liao and Li, 2019; Wang et al., 2022). Thus, promoting children’s environmental behavior could benefit both current and future environmental quality. While numerous previous studies on waste separation have focused on adults, few studies have paid attention to children. Thus, this study is one of the pioneer attempts to use an expanded TPB model to understand children’s waste separation behaviors and how they differ from those of adults. Several findings can be drawn from the study.

First, we found a paradoxical result when comparing the scores of the scales between children and adults. For the six latent variables (attitude, subjective norm, perceived behavioral control, awareness, intention, and behavior), children’s means were higher than adults. Interestingly, when came to the objective items of knowledge, the result was just the opposite, children’s correct percentage was lower than adults’. According to prior studies, this may be due to social desirability bias. When responding to self-report questions, children are more vulnerable to such effects than adults (Baxter et al., 2004; Logan et al., 2008; Krumpal, 2013; Camerini and Schulz, 2017). Therefore, when answering the self-report questions about waste separation, children would more prone to take into account social desirability, thus reporting higher scores than adults. Meanwhile, some other studies claimed that 9–13 years old was the stage when people would show the highest environmental value and behavior (Collado et al., 2015), which may be another reason for such a result. As for the waste separation knowledge, adults are the primary force separating waste in a family, children have fewer opportunities to participate in waste separation directly and deal with less types of waste than adults (Collado et al., 2015). This may be why children’s objective waste separation knowledge is lower than that of adults. The intention-behavior discrepancy is consistent with numerous studies (Zhang et al., 2019; Wang et al., 2020), and behavior can be influenced by many contextual factors in addition to subjective intention.

Second, as for the TPB variable, the only significant factor influencing children’s waste separation intention and behavior was perceived behavioral control. This result is consistent with the original TPB model (Ajzen, 1991) and many other previous studies (Chan and Bishop, 2013; de Leeuw et al., 2015; Goh et al., 2022). That is, children are more likely to engage in waste separation behavior when they feel facilitated or capable of doing so. Surprisingly, attitude and subjective norm were found to be non-significant predictor of waste separation intention and behavior, and waste separation intention also failed to predict the behavior.

Attitude was found not a reliable predictor of behavior in other studies too. Numerous studies confirmed that attitude can positively influence environmental intention (de Leeuw et al., 2015; Kumar, 2019; Zhang et al., 2019; Wang et al., 2020), while others argued that a stronger attitude may not always be leading to stronger intention (Collado et al., 2015, 2017; Casaló and Escario, 2018; Otto et al., 2019; Bechler et al., 2021; Šorytė and Pakalniškienė, 2021). Bechler et al. (2021) noted that attitude would have an effect on behavior only when it crosses the valence threshold (from positive to negative or vice versa). According to Casaló and Escario (2018), children may not have enough opportunities to engage in certain environmental behaviors, which could reinforce or weaken the translation from attitude to willingness of behavior. Collado et al. (2017) also noted that older groups are more likely than younger groups to translate their attitude into behavior.

Similarly, subjective norm being non-significant in this study is not unique. While Ajzen (1991) argued that social pressure is an important antecedent for subjective norm to work, subjective norm does not always lead to social pressure, especially in the private behavioral domain where others are invisible (Ma et al., 2018; Zhang et al., 2019; Alzubaidi et al., 2021; Yang et al., 2021), such as waste separation behavior. Furthermore, prior studies have found that children over the age of 13 are more sensitive to social pressure (Yeager et al., 2018), our samples may be not mature enough to consider what others prefer them to do.

Third, the role of two expanded variables, awareness and knowledge, in promoting waste separation intention were explored. In line with many previous studies, the greater the awareness of the consequences of not separating waste, the greater the intention (Zhang et al., 2019; Bülbül et al., 2020; Goh et al., 2022; Oturai et al., 2022). Individuals who are aware of the potentially harmful consequences of not separating waste are more concerned about their environmental behavior, thus, more likely to change their behavior mode to mitigate the harm (Zhang et al., 2019; Bülbül et al., 2020; Oturai et al., 2022). When come to the relationship between knowledge and waste separation intention, the findings of prior studies are divergent. Some researchers found a positive relationship (Pagiaslis and Krontalis, 2014; Zhang et al., 2017; Casaló et al., 2019; Cologna et al., 2022) while others disagree with these findings (Grob, 1995; de Leeuw et al., 2015; Otto et al., 2015; Otto and Pensini, 2017; Taube et al., 2021). The non-significant relationship in this study may be due to the fact that the process of knowledge acquisition is not accompanied by the action and the real environment (Otto and Pensini, 2017; Liu et al., 2020). Furthermore, simply focusing on objective knowledge could be another reason for the non-significant results. Pagiaslis and Krontalis (2014) found that subjective knowledge, rather than objective knowledge, had a significant impact on the intention to pay higher prices for eco-fuels. Similarly, Casaló et al. (2019) found that people with high subjective knowledge were more likely to engage in daily environmental behaviors.

Finally, several differences were found by comparing the path coefficients and the percentage of explained variance of the two groups. Adults’ explained variance of waste separation intention and behavior (R_Intention² = 72.7%; R_Behavior² = 53.5%) were greater than those of children (R_Intention² = 22.8%; R_Behavior² = 10.6%). Furthermore, unlike children, adults’ attitude, subjective norm, and perceived behavioral control all had a significant impact on their waste separation intention, and perceived behavioral control and intention can both had a significant impact on their waste separation behavior. This could be due to both the fewer opportunities for children to engage in waste separation practice directly, and their inability to accurately predict the consequences of their behavior (Roux et al., 2021; Šorytė and Pakalniškienė, 2021; Jeremic Stojkovic et al., 2022). Furthermore, the role of the two extended variables, awareness and knowledge, in the adults’ model, was contrary to children’s. Adults’ knowledge had a significant positive effect on waste separation intention, whereas awareness did not. Previous studies have confirmed the effect of knowledge (Meinhold and Malkus, 2005; Pagiaslis and Krontalis, 2014; Pothitou et al., 2016; Liao and Li, 2019), and the non-significant relationship between awareness and intention may be due to the lack of relevant information (Liobikienė and Juknys, 2016). Meanwhile, Fu et al. (2020) argued that situational factors have a greater impact on intention than internal motivations such as awareness.

Children are not only the important force of current waste separation but also the main drivers and policymakers of the future. Meanwhile, they can influence the waste separation behavior of adults. Hence, there is a strong need to study the factors influencing children’s waste separation behavior. To our knowledge, the present study is one of the few studies to employ an expanded model of TPB to explore children’s waste separation behavior. This expanded model takes into account knowledge and awareness in addition to origin measures of attitude, subjective norm, and perceived behavioral control as predictors of waste separation intention and self-reported behavior. Furthermore, the findings of this study have helped create a better understanding of the differences between children’s and adults’ waste separation behavior.

The study made a number of implications for environmental course developers and policymakers. First, perceived behavioral control is proved crucial to enhance children’s waste separation intention and behavior. Therefore, environmental agencies should take steps to increase their perceptions of how easy it is to engage in waste separation behavior, such as lowering the trash bins, making the bins more visible, positioning the bins closer to homes or classrooms, and placing waste separation guidance near the bins. Second, children’s waste separation knowledge is significantly lower than that of adults. Although the role of knowledge on waste separation intention is not proven, however, it is impossible to adopt the proper behavior without action-oriented knowledge. Therefore, environmental organizations and educational institutions should provide procedural knowledge to children in various ways, such as the internet and training courses. Moreover, it is better to incorporate real-world applications into the knowledge transfer process. Third, given that children’s explained variance of intention and behavior are lower than those of adults, furthermore, unlike adults, children’s intention was found to have no significant impact on behavior, schools should focus more on promoting children’s cognitive abilities such as decision making and consequence prediction. Finally, to narrow the gap between waste separation behavior and intention, authorities should provide more external conditions that facilitate waste separation for both children and adults, such as financial incentives and mandatory rules.

There are some limitations about the present study that future research can address. First, we did not include children/adolescents aged under 9 years old or 12–18 years old. Due to method and resource constraints, we decided to focus on mid-age children who are 9–12 years old to determine the factors influencing children’s waste separation behavior and explore the differences with adults. Future studies could expand the age range to explore the development patterns of waste separation behavior. Second, the study explored correlations between variables, and future research could explore causality by manipulating variables. In addition, this study collected data through self-reports and therefor may have been influenced by socially desirable answers. Incorporating objectively measured behaviors by observing and recording actual behaviors would be beneficial for future studies.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

The studies involving humans were approved by Institutional Review Board of the Institute of Psychology, Chinese Academy of Sciences. The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation in this study was provided by the participants’ legal guardians/next of kin. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

JP: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Software, Writing – original draft, Writing – review & editing. PL: Methodology, Project administration, Supervision, Validation, Writing – review & editing.