Who can be in a group? 3-to 5-year-old children construe realistic social groups through mutual intentionality

Recent research suggests that young children's causal justification for minimal group membership can be induced via a cognitive framework of mutual intentionality. That is, an individual can become a group member when both the individual and group agree to membership. Here, we investigated if children ages 3-5 understand groups formed by mutual intentions and whether they apply mutual intentions to realistic groups with varying entitative and essentialized qualities. In two studies (N = 197), we asked 3-, 4-, and 5-year-old children if a novel character could join an existing group based on intentionality (mutual, individual-, group-only) and group type (task, friends, family). We find that 4- and 5-year-olds robustly relied on mutual intentions to constitute group membership and 3-year-olds also demonstrated emerging usage of this cognitive framework. Moreover, children employed mutual intentionality across different group types, suggesting a general framework for children's understanding of different social groups.