Medical anthropology specializes in documenting the nuances of ethnomedical systems across cultures and works with stakeholders at various levels of socio-ecological systems to address illness-related problems and promote health innovations. While adult perceptions are important to understand, children are also stakeholders in their communities and can play important roles in health interventions and thus also need to be prioritized in research and community health interventions. Children’s illness perceptions develop early in life and are shaped by diverse cultural beliefs and socio-ecological settings. Here I explore and build knowledge about Maasai agro-pastoralist children’s ethnobiological notions of illness in northern Tanzania and conduct a health intervention with schoolchildren in the research community. Mixed methods were used to learn about Maasai children’s understandings of contagion and contamination and salient illnesses and their etiologies, which were compared to adult Maasai perspectives. Maasai often listed illnesses that impact children, such as diarrhea, eye problems, tonsils, and skin sores like eriri (small pimples) and sada (big blisters). Of the illnesses reported for both adults and children, some had age-specific etiologies, such as food consumption and ulcers being the cause of stomach problems among children versus adults, respectively. Like adults, Maasai children reported natural and supernatural explanations for illnesses, contagions and contaminations, but some of their explanations for some of the illnesses differed from adult explanations. Responses also included local ethnoecological concepts about illness, such as wind. Education level influenced Maasai children’s etiological beliefs, contagion and contamination knowledge, and, in our follow-up of the health intervention, retention of our health education material. Access to formal education promotes literacy and math skills and introduces students to biomedical concepts of pathogenic invisible organisms, all of which can promote health and benefit the adoption of health innovations. Like other anthropological work, particularly within tropical medicine, children can thus be essential for health and disease-control efforts, especially in communities with low adult literacy, such as the Maasai. A medical anthropology approach is important to help shape prevention efforts and initiatives by tailoring health innovations to the cultural and developmental context of children and adults within target communities.