Symbolic counting skills promote numerically-sensitive intolerance for selfishness

One of the most pervasive human interests is the acquisition of norms surrounding fairness—young children care about equality, enforce it in their behavior, and punish those who don’t behave accordingly. Though the fact that children care about fairness is well-documented, less is understood about the types of fairness norms that children endorse: In this work, across two studies with preschool-aged children (ages 2.5-6; N = 123), we document a developmental shift towards precision in sharing norms, both in rejecting extreme inequalities (i.e. giving none) and increased endorsement of exact equality (distributing exactly equal amounts). Children’s symbolic counting skills (i.e., acquisition of the cardinal principle) predicted this shift across two studies, even when accounting for approximate number acuity and symbolic and non-symbolic understanding of null sets, though this effect emerged only for children’s tolerance of selfish sharing—most forms of generous sharing were tolerated regardless of numerical abilities. Our results suggest a developmental shift from an abstract notion of learning to an increasingly precise notion of equality as children acquire symbolic counting skills.