Past research suggests that children favour their in-group members over out-group members as indicated by selective prosociality such as sharing or social inclusion. This preregistered study examined how playing a cooperative, competitive or solitary game influences German 4- to 6-year-olds’ in-group bias and their general willingness to act prosocially, independent of the recipient's group membership ( N = 144). After playing the game, experimenters introduced minimal groups and assessed children's sharing with an in-group and an out-group member as well as their social inclusion of an out-group member into an in-group interaction. Furthermore, we assessed children's physical engagement and parents' social dominance orientation (SDO)—a scale indicating the preference for inequality among social groups—to learn more about inter-individual differences in children's prosocial behaviours. Results suggest that children showed a stronger physical engagement while playing competitively as compared with cooperatively or alone. The different gaming contexts did not impact children's subsequent in-group bias or general willingness to act prosocially. Parental SDO was not linked to children's prosocial behaviours. These results indicate that competition can immediately affect children's behaviour while playing but raise doubt on the importance of cooperative and competitive play for children's subsequent intergroup and prosocial behaviour.