The aim of this article is to explore the social dimension of sustainable development through children’s expressions of belonging in peer communities in preschool. Social sustainability and sustainable communities emphasize practices, human activity, and interactions that are equitable, inclusive, and sustainable, and preschool provides children with experiences of participation in collective groups and networks. Belonging to a community is an existential need and belonging, itself, is a relational phenomenon. Belonging is connected to power; the notion of “us” sets boundaries and creates a “them”. Based on Yuval-Davis’ analytical concepts and using video observation of children’s (aged 3–5) free play, this article explores children’s belonging in peer communities. This study contributes new knowledge in the field of social sustainability by illuminating communities of belonging built on closeness, conflict/negotiations, and joyfulness. Together, these elements embody experiences of importance to children’s belonging. A common thread running through these communities is the relationship between the individual and the community.