Emotions are commitment devices that play a crucial role in regulating children's social interactions with peers towards shared, cooperative goals. In the context of cooperation, emotions motivate one's own behaviour to help and care for others and regulate others' behaviour in response to one's emotional expression (Frank, Reference Frank1988; Keltner, Kogan, Piff, & Saturn, Reference Keltner, Kogan, Piff and Saturn2014; Parkinson, Reference Parkinson1996; Vaish & Hepach, Reference Vaish and Hepach2020). From early in ontogeny, emotions underlie the two-step process involved in cooperation: generating benefits and distributing benefits (Warneken, Reference Warneken2018). Grossmann presents an intriguing developmental account of how children's fear expression, typically classified as a negative emotion, has in fact positive outcomes because it motivates cooperation from caregivers. But there is no reason to assume that children's expression of fear and attention to fear in others is limited to regulating cooperation between infants and adult caretakers. Here we offer a critical reflection on how children's fear proneness may regulate their cooperative interactions – specifically their helping and concern for fairness towards peers – beyond provisioning help from caretakers.

In the first years of life, children's interactions are not exclusively cooperative and include bouts of mild aggression accompanied by negative emotions such as frustration and anger (Dahl, Reference Dahl2016; Hay & Ross, Reference Hay and Ross1982). Such negative interactions are not so much driven by antisocial motivations but can rather arise from children's curiosity and interest in their peers. Should such “exchanges” of toys or “explorations” of personal space escalate, caretakers offer help and resolve such conflicts which is, to some extent, motivated by children's fearful expression. Despite the temperamental volatility evident in young children's peer interactions, children do help and share with peers and their ability to coordinate joint actions develops into cooperative activities by the end of the second year of life (Brownell, Ramani, & Zerwas, Reference Brownell, Ramani and Zerwas2006; Eckerman, Davis, & Didow, Reference Eckerman, Davis and Didow1989; Hepach, Kante, & Tomasello, Reference Hepach, Kante and Tomasello2017). Cooperation with peers thus presents a scaffold for children's interactions and mutual expectations. Children's expressed fearfulness, moreover, can elicit cooperation from peers and children's attention to fear in their peers may predict their own cooperation. Indeed, Grossmann cites evidence, much from his own pioneering work, to demonstrate a link between children's attention to fear in others and their own helping and sharing behaviour (Grossmann et al., Reference Grossmann, Missana and Krol2018; Rajhans, Jessen, Missana, & Grossmann, Reference Rajhans, Jessen, Missana and Grossmann2016).

The widening of children's social circle, the increased complexity in their peer interactions, and their elevated cognitive capacity for reputation management (see Engelmann & Rapp, Reference Engelmann and Rapp2018, for a review) all increase children's concern for or even fear of others' evaluations. Emotions such as shame are elicited when children think that they have failed to meet a (social) standard, especially if such failures are observed by others. By contrast, pride is elicited when children feel that they have met or even exceeded a social standard (e.g., Lewis et al., Reference Lewis, Alessandri and Sullivan1992; Stipek, Recchia, McClintic, & Lewis, Reference Stipek, Recchia, McClintic and Lewis1992). Self-conscious emotions may thus offer a means for children to express how much they value cooperative relationships with peers starting during the preschool years. The nature and development of such emotions can be examined when presenting children with situations in which they receive undeserving help, unfair distributions of resources, or make unjustified requests.

At 4 years of age, children express less positive emotions, a reduction in upper-body posture, when they were helped but a more needy peer was not (Hepach & Tomasello, Reference Hepach and Tomasello2020). Five-year-old children showed more negative emotions – through a lowered-body posture – compared to 4-year-olds when they failed to complete tasks both for themselves and for others (Gerdemann, Tippmann, Dietrich, Engelmann, & Hepach, Reference Gerdemann, Tippmann, Dietrich, Engelmann and Hepach2022c). In addition to expressing negative emotions in response to unsuccessful helping and receiving undeserving help, 5- but not 3-year-old children's posture is lowered when making justified requests, that is, asking someone for a tool if that person needs the tool more than the child (Waddington, Hepach, Jackson, & Köymen, Reference Waddington, Hepach, Jackson and Köymen2022). The most systematic investigation to date of changes in children's body posture in the context of (un)fairness demonstrated that between 4 and 10 years of age, children's emotions expressed in response to receiving more of a reward than a peer (i.e., advantageously unequal outcomes) became more negative with increasing age. Conversely, children's emotions became more positive with age following equal distributions of resources (Gerdemann, McAuliffe, Blake, Haun, & Hepach, Reference Gerdemann, McAuliffe, Blake, Haun and Hepach2022a). Together, these findings suggest that emotions can regulate children's cooperative interactions although more research is needed to specify this relation. Receiving help or resources may be beneficial for the individual child but if the outcome is undeserving or unfair, then this may strain the cooperative relationship with peers. Children may risk being viewed as more concerned for their own gains even if it comes at a cost to others. In the context of cooperation, signalling one's fear of a peers' evaluation and rejection, for example, through lowered-body posture, may have an adaptive value for children who aspire to good terms with their peers (see also Gerdemann, Büchner, & Hepach, Reference Gerdemann, Büchner and Hepach2022b).

In summary, one direction for future research could be to test the implications of the fearful ape hypothesis in the context of children's peer interactions. In addition to soliciting help from caretakers, peer cooperation may constitute a setting in which children respond to each other's expression of fear to solicit mutual aid. Cooperation may even reduce fear much like it increases positive emotions and sharing (Hamann, Bender, & Tomasello, Reference Hamann, Bender and Tomasello2014; Lennon & Eisenberg, Reference Lennon and Eisenberg1987; Stengelin, Hepach, & Haun, Reference Stengelin, Hepach and Haun2020). The emergence of self-conscious emotions such as shame in early childhood may build on children's fear expression observed in infancy yet may arguably constitute a qualitatively more complex emotional experience. One way of testing the hypothesized developmental relation between these two kinds of emotions would be to relate the early expression of fear – assessed using methods pioneered by Grossmann and colleagues – to children's social emotions expressed in the context of children's peer cooperation. This would be one way to assert whether the expression of shame, in middle childhood, elicits cooperation from peers in the same way that the expression of fear in early childhood elicits caretaking from adults.