It has been shown that with age, US children become more likely to prefer equal over unequal allocations and do so in an impartial way for both ingroup and outgroup members. However, it is possible that such findings are based on norms of impartiality that are more common in Western societies than in collectivistic societies which place a greater emphasis on group loyalty. For example, children from a collectivist society might endorse ingroup-favoring allocations more than equal allocations or outgroup-favoring ones. In this pre-registered study, n = 205 5- to 12-year-olds from the US and South Korea saw hypothetical scenarios in which a child divided resources (e.g., chocolates) between their ingroup and outgroup. Group membership was manipulated using a minimal group paradigm based on team colors. Children evaluated equal, ingroup-favoring, and outgroup-favoring allocations. Results showed that children from both samples overall evaluated equal allocations most positively. However, Korean children judged ingroup-favoring allocations more acceptable and less deserving of punishment than did US peers. Both results were consistent across ages, suggesting the developmental stability of these effects from middle childhood into early adolescence. We discuss how the current results provide insight into cross-cultural differences in fairness norms.