For kids up to age three or four, this is indeed the case. Fish, especially oily ones, such as salmon, are packed with omega-3 fatty acids, including DHA (docosahexaenoic acid). "DHA is particularly beneficial in the first two years of life for brain development, cognition, and visual acuity," says Beverly Hills pediatrician Scott W. Cohen, the author of Eat, Sleep, Poop: A Common Sense Guide to Your Baby's First Year ($16, amazon.com). And a 2008 study in Clinical Pediatrics showed an increase in vocabulary and comprehension for four-year-olds who were given daily DHA supplements. Omega-3 options for the fish-phobic? Try avocados, walnuts, and canola oil.