I have a cohesive research programme directed at understanding socio-environmental associates and predictors of children’s activity and body size. My vision is to be an international expert in policy-relevant research in children’s health and built environments. Research objectives are to assess the impact of environmental changes on children’s health behaviours and outcomes. Children’s activity, active travel, and body size will be assessed across four conditions: (1) Intensive, neighbourhood wide infrastructural intervention, (2) Light, neighbourhood wide infrastructural intervention, (3) A socio-demographically matched control neighbourhood, and (4) Nationally representative control data. Physical inactivity is the second greatest cause of non-communicable disease in NZ. A third of NZ children are overweight or obese. Built environments are likely to have greater, and more sustained, influences on behaviour than individual factors. This research can fill an important knowledge gap, to understand what type of environmental intervention produces optimal health behaviours and outcomes in children.