Group membership is a strong driver of everyday life in humans, influencing similarity judgments, trust choices, and learning processes. However, its ontogenetic development remains to be understood. This study investigated how group membership, age, sex, and identification with a team influenced 39- to 60-month-old children (N = 94) in a series of similarity, trust, and learning tasks. Group membership had the most influence on similarity and trust tasks, strongly biasing choices toward in-groups. In contrast, prior experience and identification with the team were the most important factors in the learning tasks. Finally, overimitation occurred most when the children's team, but not the opposite, displayed meaningless actions. Future work must investigate how these cognitive abilities combine during development to facilitate cultural processes.