This paper suggests that a principal-agent perspective may be one of several useful ways of analyzing the family. The principal-agent literature has so far ignored an important set of cases where the principal is incapable of defining and defending her own interests, and so is assigned an agent by law or custom. This paper applies principal-agent analysis to one such case, the family, where the child is taken as the principal and the parent is her agent. The principal-agent problem within families creates a prima facie case for certain state interventions to protect the interests of child-principals. The principal-agent perspective on the family sheds new light on two old debates: about provision of state welfare services in cash or in kind, and about user fees for social services.