The specificity of reciprocity: Young children reciprocate more generously to those who intentionally benefit them.

Young children engage in direct reciprocity, but the mechanisms underlying such reciprocity remain unclear. In particular, prior work leaves unclear whether children's reciprocity is simply a response to receiving benefits (regardless of whether the benefits were intended) or driven by a mechanism of rewarding or preferring all benefactors (regardless of whom they benefited). Alternatively, perhaps children engage in genuine reciprocity such that they are particularly prosocial toward benefactors who intentionally provided them with benefits. Our findings support this third, richer possibility; the 3-year-olds who received benefits through the good intentions of a benefactor were subsequently more generous toward the benefactor than children who either (a) received the same benefits from the benefactor unintentionally or (b) observed the benefactor bestow the same benefits on another individual. Thus, young children are especially motivated to benefit those who have demonstrated goodwill toward them, suggesting, as one possible mechanism, an early sense of gratitude.