The health of future children should be of prime importance to today’s generation. Accurate projections of child health this century are essential to ensure that future children have the best opportunity for healthy lives. United Nations (UN) projections of future child mortality to 2100 rely upon extrapolating past child mortality data and ignore the expected health consequences of environmental deterioration and rapid population increases. Our corrections to the UN projections show that infant and child mortality will soon begin to increase rapidly, especially in low- and middle-income countries. Our findings have the potential to catalyse governments to take urgent action.