Children are increasingly described as agents and agency is important to arguments for children's rights and participation. Yet agency is rarely defined or theorised in childhood studies. This article reviews common uses and meanings of agency and argues that critical, social conceptualisations have yet to be extensively taken up in childhood studies but offer much to the field. Based on the work of Giddens, his critics and feminist theory, I propose a model of agency that is more ambivalent than that usually presented in childhood studies. Given the conventional emphasis of agency on articulation, rationality and strategy, a failure to incorporate a critical, embodied, engendered, material account of agency into childhood studies risks reinscribing a model in which privileged children will be accorded more agency than those who do not display rationality and choice in conventional ways.