Debate about the definition of a ‘child’ occurs in multi-disciplinary contexts, most recently located in the new sociology of childhood where social constructionism is the dominant discourse. Given that the child’s voice has become an increasingly valued component of research, this paper reports on one aspect of a study which explored how 7–11-year-olds (N = 56) defined and understood the concept of ‘a child’. Data were categorised into four types: physical, behavioural, lifestyle and criteria-referenced descriptors. Dominant theoretical elements such as agency, social construction, relational understanding and notions of themselves as beings were evident in the children’s responses. However, the importance of the biological and developmental bases of childhood and their sense of becoming adults were stronger than is sometimes acknowledged in the literature. The implications for education of these two digressions from contemporary theoretical discourse are considered in light of the Cambridge Primary Review which calls for a reshaping of primary education and initial teacher training in England to include childhood as a central concept.