After decades of increases, the prevalence of childhood obesity has declined in the past decade in New York City, as measured in children participating in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) and public school students, with the greatest reductions occurring in the youngest children. Possible explanations were changes in demographics; WIC, day care, and school food policies; citywide obesity prevention policies, media messages; and family and community food consumption. Although the decreases cannot be attributed to any one cause, the most plausible explanation is changes in food consumption at home, prompted by media messages and reinforced by school and child care center policy changes. Continued media messages and policy changes are needed to sustain these improvements and extend them to other age groups.