The risks of climate change to children have been widely discussed, but the risks of overpopulation have not been similarly scrutinised. Projections of the health and mortality rates of infants and children have largely ignored overpopulation; for example, the United Nation's projections of infant mortality to 2100 disregard the influences of rapidly increasing populations in low-and middle-income countries and a deteriorating climate. In this paper, we first summarise the evidence that a large and growing human population will increase child mortality, and compromise health and wellbeing this century. Population growth increases the pace and magnitude of climate change because the degree of climate disruption is a product of per-capita consumption and total population size. Population growth also increases overcrowding, which in turn increases local and global air pollution, disease transmission, and resource scarcity, all of which have disproportionate effects on children compared to adults. To gain insight into the potential risks that children will face this century, we analysed the United Nation's Medium and High population projections for this century to show that between 9.91 billion and 14.49 billion children will be born from 2022 to 2100, and that most (> 60%) will be born in sub-Saharan Africa and Central/South Asia (6.19 billion and 9.10 billion, 62.5% and 61.4% of all births, Medium and High projections, respectively), where malnutrition is already high and capacity lowest to increase crop yields accordingly. We then identify areas where future child mortality can be expected to be higher than current predictions. We show that the lowest-income nations with the highest population growth have the fewest resources to protect increasing numbers of children from the deteriorating climate and the risks of overcrowding. We emphasise the urgent need for appropriate, quality, free, non-coercive, familyplanning services to be universally available to allow men and women the opportunity to choose the size of their family. In summary, we provide the first evaluation of the evidence that overpopulation is already adversely affecting children and the evidence that there will be increasingly serious consequences for children if population growth continues at its current pace.