This study examined preschoolers' social inclusion--the active involvement of new partners into social interactions--in different intergroup contexts. Using an interactive paradigm, 3- to 5-year-old German children played a ball-tossing game with 2 puppets in which 1 puppet initiated the game with the child and another approached the game. In Study 1 (N = 144), the initiator was from an ingroup while an outgroup puppet approached the game (ingroup/outgroup condition) or the child and the 2 puppets did not have any group membership (control condition). Social inclusion was assessed by analyzing whether and how children included the approaching puppet into the game. Results revealed that children were more inclusive with increasing age. Across age, children were less willing to include the approaching puppet in the intergroup context as compared to the control context. To further investigate whether the difference between conditions was driven by a preference for the ingroup or a derogation of the outgroup, a second study (N = 72) was conducted. Here, the initiating puppet was neutral (i.e., no group membership) and the approaching puppet was from an outgroup (neutral/outgroup condition). In this condition, social inclusion was in between the 2 conditions of Study 1. Further, the developmental trajectory found in Study 1 could be replicated in Study 2 such that children were more likely to include the approaching puppet with increasing age. These results suggest that children's willingness to include others increases over preschool age and is influenced by both ingroup favoritism and outgroup derogation.