Cooperation, the acting together for a common end or purpose (Tuomela, 1993), is an essential aspect of human life, it is necessary to its survival as well as to its flourishing. In order to work, it requires good skills in partner choice, allowing the individual to stay away from free-riders, non-reciprocators, and other unfair and harmful individuals (Fehr et al., 2008; Baumard et al., 2013; Shaw et al., 2014). Cooperation also requires an understanding of others’ goals and it is grounded in social motivations for helping and sharing with others (Tomasello, 2007). What are the origins of these motivations and evaluation skills? Recent works on infants’ social preferences and expectations help us to address this question and constraint nativist and empiricist models of cognitive architecture and development (Margolis and Laurence, 2013; Tomasello and Vaish, 2013). In the first year, infants prefer agents who help others to agents who hinder others (Hamlin et al., 2007, 2011; Hamlin, 2013, 2015) and agents who comfort rather than harm (Buon et al., 2014; see also Holvoet et al., 2016). By 10 months, they expect agents to perform equal distributions (Meristo et al., 2016) and to act positively toward fair donors and negatively toward unfair donors (Meristo and Surian, 2013, 2014).

In their second year, infants also evaluate distributions of resources performed toward third parties (Schmidt and Sommerville, 2011; Sommerville et al., 2013), choose agents who perform equal rather than unequal distributions (Geraci and Surian, 2011; Burns and Sommerville, 2014) and take relative merit into account when witnessing equal and unequal distributions (Sloane et al., 2012). Also, they associate praise and admonishments to fair and unfair distributors, respectively (DesChamps et al., 2015). Overall, this evidence suggests that they assign a positive valence to fair distributions and expect that positive and negative actions directed toward distributors will conform to reciprocity principles (Baillargeon et al., 2015).

Most of the available evidence on infants’ emerging ability to evaluate distributions comes from looking times. In the present study we looked for converging evidence from a more active dependent measure, namely infants’ prosocial actions performed toward agents that have just distributed resources fairly or unfairly. Prosociality may be expressed through a variety of activities, such as giving instrumental help and sharing resources, which can be observed from early childhood. Toddlers display spontaneous helping when see an adult having trouble achieving a goal (e.g., Warneken and Tomasello, 2006, 2007) and they display sharing actions when they recognize another individual’s lack of a desired material good (Olson and Spelke, 2008; Svetlova et al., 2010; Dunfield et al., 2011).

One crucial aspect of early prosocial actions is their selectivity (Kuhlmeier et al., 2014). Dunfield and Kuhlmeier (2010) found that 21-month-olds selectively picked up an out-of-reach object for an actor who, in a previous interaction, intended to provide them with a desired toy over one who did not. Toddlers selected the recipient of their helping behavior based on the helpee’s intention to deliver toy, even if he or she failed to deliver it. Likewise, 3-year-olds selectively avoid helping those who caused harm, or even simply intended to cause harm to others (Vaish et al., 2010). Previous findings also indicate that toddlers and young children select the recipient of their sharing behaviors relying on recipients’ previous actions (Olson and Spelke, 2008; Kenward and Dahl, 2011; Kanngiesser and Warneken, 2012).

In this study, we examined whether selective helping in toddlers is linked to previous distributive actions. We recorded their helping behaviors toward agents that performed either equal or unequal allocations of resources. Previous results on toddlers’ propensity to help prosocial agents and evaluate distributors lead to the prediction that they would be more likely to help a fair than an unfair distributor.

None of the counterbalanced factors had a significant effect on children’s choices (p’s > 0.07). Children showed no uncertainty in their choices by starting to give the ball to one actress, but finally giving it to the other one. Eleven children (25%) did not help either actress and the rest (n = 33, 75%) helped one of them. This helping rate is similar to the rate found in previous experiments (Dunfield and Kuhlmeier, 2010). Twenty-four children (72.7%) helped the fair actress and the other 9 (27.3%) helped the unfair one, binomial test, p = 0.014.

Considering the wide age range of the participants, we split the sample in two age groups: 22 20-month-olds (11 girls; mean age = 20 months, 29 days; age range: 18 months, 12 days to 23 months, 4 days) and 22 30-month-olds (11 girls; mean age = 30 months, 8 days; age range: 27 months, 17 days to 33 months, 6 days). The preference for the fair actress in the two age groups was very similar, Fisher exact test, p > 0.5, OR = 1.24 95% CI [0.21, 7.94]. At 20 months, 17 children (77.3%) helped one of the actresses. Twelve children (71%) helped the fair actress, and the other 5 (29%) helped the unfair actress. At 30 months, 16 children (72.7%) helped one of the actresses, 12 (75%) helped the fair actress and 4 (25%) the unfair one. Due to the small sample size, the p-values of the separate binomial tests were above the 0.05 significance level and reached trend level in the older group (p = 0.142 and p = 0.076, respectively).

These results reveal that toddlers’ selective helping is linked to agents’ previous distributive actions. This finding contributes to our understanding of early social cognition in two important ways. First, it shows that selective helping is not constrained solely by agents’ helping or hindering actions, but also by their distributive behaviors previously directed toward third parties. Second, it points out that toddlers’ sensitivity to agents’ distributive actions may inform processes underpinning their prosocial choices, thus providing crucial converging evidence to support recent proposals on the early emergence of a sense of fairness.

Preferences for prosocial agents have been reported in several experiments, even in preverbal infants, using scenarios in which helpers facilitate a third party in achieving a goal while hinderers prevent the goal achievement (e.g., Hamlin et al., 2007, 2011). However, a preference for fair distributors has been reported in only two previous studies. This preference was found at 15–16 months, but not before (Geraci and Surian, 2011; Burns and Sommerville, 2014). Therefore, the present study provides an important contribution to the literature on infants’ sense of fairness by consolidating and extending the effects found with paradigms that require an action response that reveals a preference for a certain type of distributors.

One limitation of the present study derives from the relatively small sample size. An interesting goal for future studies on infants’ and toddlers’ selective helping will be to employ longitudinal designs and to assess whether their preference for fair individuals develops simultaneously or later than their preference for agents that comfort (Buon et al., 2014) and help others (Hamlin, 2013). Future works could extend this result in several interesting ways. By presenting equal and unequal distributors paired with neutral agents one could test whether the bias found in the present study was due to a preference for helping the fair agent or to avoid the unfair one (Hamlin et al., 2007; Vaish et al., 2010), or both. It would be also useful to test children in a non-distributive control condition, like in Meristo et al. (2016, Exp. 3), in order to assess the possible effect due to the symmetric and asymmetric interactions displayed by the two agents.

Moreover, one way to cast light on the underlying mechanism would be to investigate whether distributors’ intentions to perform equal or unequal distributions can affect toddler’s selective helping, regardless of the final outcome of their attempts (Margoni and Surian, 2016). This would also help to assess the robustness and generality of toddlers’ intention-mediated selecting helping, previously found (Dunfield and Kuhlmeier, 2010) in harming and helping scenarios.

Both authors contributed equally to hypothesis generation, experimental design, data collection and analyses, and writing of the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer AP and handling Editor declared their shared affiliation, and the handling Editor states that the process nevertheless met the standards of a fair and objective review.