Open access. From birth, children living in disadvantaged socioeconomic circumstances (SECs) suffer from worse health than their more advantaged peers. The pathways through which SECs influence children’s health are complex and inter-related, but in general are driven by differences in the distribution of power and resources that determine the economic, material and psychosocial conditions in which children grow up. A better understanding of why children from more disadvantaged backgrounds have worse health and how interventions work, for whom and in what contexts, will help to reduce these unfair differences. Macro-level change is also required, including the reduction of child poverty through improved social security systems and employment opportunities, and continued investment in high-quality and accessible services (eg, childcare, key workers, children’s centres and healthy school environments). Child health professionals can play a crucial role by being mindful of the social determinants of health in their daily practice, and through advocating for more equitable and child-focussed resource allocation.