Recent research has produced new insights into the early development of social cognition and social learning. Even very young children learn and understand social activities as governed by conventional norms that (a) are arbitrary and shared by the community, (b) have normative force and apply to all participants, and (c) are valid in context-relative ways. Importantly, such understanding is revealed both in the fact that children themselves follow the norms, and in the fact that they actively enforce them toward third parties. Human social cognition thus has a fundamental normative dimension that begins early. This norm psychology plausibly evolved due to its role in stabilizing group coordination and cooperation, and is one of the foundations of what is uniquely human social learning and culture.