This paper outlines a dialectical conceptualisation of children's agency for the purposes of multidisciplinary educational theory and practice. We illuminate five contradictory but connected dimensions of children's agency, or "the dialectics of agency," identified from theoretical debate between sociologically and psychologically oriented educational literature: Agency (1) as enacted and imagined; (2) as situatively emergent and progressively developmental; (3) as dependence and separation; (4) as mastery and submission; and (5) as control and freedom. We examine these contradictions "at work" in an ethnographic early education case study. We argue that the children's struggles towards agency and adults' efforts and failures to support children in their struggles can be conceptualised as a dialectical movement that has a potential to develop the educational practice itself. Our dialectical reading of both data and theory helps to highlight the challenges the practitioners face when supporting children's agency and the solutions they implement when doing so.