A foundational mechanism underlying human cooperation is reciprocity. In the context of repeated interactions with others, it is not always clear the degree to which in-kind responses reflect responsiveness to partners' prior behaviors ("reactive" responses), an interest unrelated to the partner ("nonreactive" responses), or any combination of the two. To disentangle these two types of responses, we presented children with sequential, one-shot, and costly interactions between themselves and either egalitarian or selfish peers. Study 1 tested direct, generalized, and normative reciprocal scenarios (N = 144 seven-year-old German children; 50% girls and 50% boys), finding that "nonreactive" responses were dominant for boys and manifested in the form of "selfish" resource distribution. Among girls, "reactive" responses were dominant and manifested in the form of in-kind resource distribution. Study 2 addressed even younger German children (N = 144; 4- to 8-year-old German children; 50% girls and 50% boys), exposing the same phenomenon among 4-year-olds, but not among 5.5-year-olds. Study 3 addressed 7-year-old Israeli children (N = 95; 49% girls and 51% boys), and replicated the basic phenomenon, with an additional cultural variation. The early emergence of gender differences in reciprocity and implications are discussed in cultural, socio-developmental, and evolutionary accounts.