'Well-being' is increasingly used in child rights discourses and early childhood education (ECE) policy contexts as a desirable outcome for young children. In spite of its ubiquitous use, however, child well-being remains largely under-theorised, thereby contributing to implicit understandings within policy arenas. This paper contributes to attempts to address this gap by proposing a theoretical framework of child well-being. The framework is developed in stages. First, two prominent approaches to well-being are described: distributive and relational approaches. Distributive approaches are subdivided into primary goods theory and capability theory. These theories focus on differential approaches to resource distribution. Relational approaches to well-being are then considered. These focus on the intrinsic importance of the processes of well-being. Second, the concepts privileged by each of these well-being theories are further developed into a framework by reflecting on children's rights to provision, protection and participation as promoted by the United Nations Convention on the Rights of the Child. Following this, the framework is used to analyse ECE policy with a specific focus on the Early Years Foundation Stage (EYFS) curriculum and measurement requirements. Academic literatures examining ECE policy is then reviewed to extrapolate understandings of the potential implications of this policy for young children's well-being. The findings suggest that the EYFS theorises well-being in ways that are limited and may be limiting of young children's well beings and doings. The associated measurement practices and curriculum goals, in particular, may undermine practice supportive of young children's well-being.