Schools are increasingly positioned as sites for intervening on the bodies and minds of children in the here and now in order to bring about health gain for the future. Public health interventions for schools bring together coalitions of commercial, statutory and philanthropic actors with children and their teachers and carers. Drawing on ethnographic case studies in London, UK, this paper explores two such interventions: one aiming to increase levels of physical activity and one to reduce exposure to air pollution. Both interventions not only evoke care for children’s own current and future wellbeing but also fold in imaginaries of collective health futures, which orient and legitimise particular intervention logics and actions. As interventions unfold, children are recruited as monitors of health risks in the present. They are also positioned as risk ambassadors, who will leverage care about unhealthy environments and lifestyles across space, to risky domestic environments, and into imagined health futures. These ‘futuring’ school‐based interventions open up small alternative spaces in which imaginaries of collective and resistant public health practices emerge. However, in the here and now, children appear to be bearing a disproportionate burden of responsibility, as ambassadors for, and imagined saviours of, public and environmental health.