Given its importance for the emergence of intergroup conflict, the development of other-regarding preferences toward in-group and out-group members has received increasing attention from various disciplines. The present study investigates children’s other-regarding preferences toward in-group and out-group members when allocating resources with positive and negative valence. The 6- and 8-year-olds’ (N = 92) task was to allocate resources to themselves versus to an in-group or an out-group member. They demonstrated prosociality more frequently toward in-group than toward out-group recipients and more frequently when positive rather than negative resources were involved. Whereas the importance of the recipient’s group membership increased with participants’ age, the importance of resource valence decreased. Furthermore, older children, but not younger ones, were more prosocial toward in-group than out-group members in the allocation of negative resources. These findings help to understand the psychological determinants and the ontogenetic origins of other-regarding preferences toward in-group versus out-group members and, hence, individual engagement in intergroup conflict.