It has been suggested that the best method for avoiding poor mental health outcomes is to build and promote positive outcomes right from the very start of life. The goal then shifts from treating problems after they have occurred, to a model enabling the formation and promotion of positive mental health outcomes. The field of the developmental origins of health and disease (DOHaD) focuses on prenatal influences as a crucial point in development. Only very recently have DOHaD researchers merged with those in mental health research to consider the effect of intrauterine exposures on the child's long-term behavioural and emotional well-being. This article examines the history of research on early-life influences on later mental health, and summarises research on numerous risk factors present in the prenatal period that are linked to an increased risk for mental health problems throughout childhood, including stress, cigarette smoking, alcohol consumption, vitamin D deficiency, and poverty. By encouraging maternal health and wellbeing during pregnancy and beyond, this field of research has immense significance at both theoretical and practical levels for understanding and addressing the effect of common exposures on child mental health.