Early emotional and cognitive development are key to children reaching their full potential and represent our best chance to improve the health and productivity of Canadians. As brain plasticity decreases with age, prenatal interventions represent the most efficient and effective means by which child neurodevelopment can be optimized. Prenatal interventions therefore hold immense promise for reducing disease burden, although most research is observational. Women enrolled in the Be Healthy in Pregnancy randomized control trial are recruited from the community and randomly assigned to nutrition+exercise and usual care groups at 14 weeks gestation. Our nutrition+exercise intervention consists of a customized nutrition and exercise program while control group mothers receive usual pregnancy care. The primary outcome of cognition and emotion regulation in children will be assessed using gold standard scales, neurophysiological assessments, laboratory tasks and informant reports. If our nutrition+exercise intervention improves child cognition and self-regulation, it could prevent or ameliorate problems with children’s cognitive development, their ability to manage their emotions, attention, and behaviour with benefits for Canadian families, our healthcare system, and society.