The present study investigated age-related changes in the intergroup allocation of resources depending on whether the ingroup norm was competitive or cooperative. Participants included children (Mage = 8.69), adolescents (Mage = 13.81), and adults (Mage = 20.89), (N = 263) who were inducted into simulated groups and informed about an ingroup norm of either cooperation or competition. The goal context for the resource allocation task was either prosocial (to benefit the welfare of animals in a charity event) or group focused (to win a national interschool competition). They were then asked to allocate resources between an ingroup and outgroup, and to justify their allocation. The findings showed that children allocated significantly more resources to their ingroup in order to achieve a prosocial goal, but only when the ingroup norm was competitive. In contrast, adolescents and adults allocated resources equally irrespective of the ingroup norm. These findings showed that children prioritized the moral goal of welfare over that of fairness when their ingroup favored competition, while adolescents and adults always prioritized fairness. Older participants justified their equal allocation with greater reference to the importance of fair competition. This study demonstrated an important developmental shift in how the prioritization of moral goals during intergroup resource allocation is influenced by ingroup norms of competition and cooperation.