The major health challenges facing children and adolescents increasingly reflect chronic problems that have complex biopsychosocial and environmental dimensions.1 In high-income countries, nearly a quarter of children and adolescents are overweight or obese,2 up to a quarter experience a mental disorder in any given year,3 allergic diseases continue to rise4 and life-threatening diseases such as cancer remain a major problem.5 Overall, children and young people from disadvantaged backgrounds are disproportionately impacted by adverse health and developmental outcomes6,7 and these disparities are expected to be further exacerbated in the context of the COVID-19 pandemic.8 Despite their burden and impact on health pathways across the life course,9,10 the origins of many of the major health issues facing children and adolescents are not yet well understood. This limits our capacity to realize opportunities for early prevention and intervention (e.g. on factors such as social disadvantage and infection) that may have cumulative health benefits over the life course.10