Omega-3 and omega-6 long-chain polyunsaturated fatty acids (LCPUFA) are critical for infant and childhood brain development, but levels of the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are often low in the Western diet. Increasing evidence from both epidemiological and intervention studies, reviewed here, indicates that DHA supplementation, during pregnancy, lactation, or childhood plays an important role in childhood neurodevelopment. Arachidonic acid (ARA) is also important for infant growth and development. Several studies have demonstrated positive associations between blood DHA levels and improvements on tests of cognitive and visual function in healthy children. Controlled trials also have shown that supplementation with DHA and EPA may help in the management of childhood psychiatric disorders, and improve visual and motor functions in children with phenylketonuria. In all studies, DHA and EPA supplementation is typically well tolerated. Further research is needed to determine optimal doses for efficacy at different developmental ages. The potential long-term benefits of early LCPUFA supplementation also require consideration.