Multiple interventions have been designed to decrease mortality and disability in children. Among these, breastfeeding is the most cost-effective intervention for protecting children against diarrhea and all causes of mortality. Human milk is uniquely suited to the human infant, both in its nutritional composition and in the nonnutritive bioactive factors that promote survival and healthy development. Suboptimal breastfeeding has been linked with numerous adverse child health outcomes including increased incidence of diarrhea and pneumonia. This review provides an update regarding recent studies on the effect of breastfeeding on diarrhea morbidity and mortality in children in developing countries, describes major human milk components responsible for this protective effect (oligosaccharides, secretory immunoglobulins, lactoferrin, bacterial microbiota, etc.), and highlights areas for future research in this topic. Breastfeeding promotion remains an intervention of enormous public health potential to decrease global mortality and promote better growth and neurodevelopment in children.