The Healthy, Hunger-Free Kids Act of 2010 strengthened nutrition standards for meals and beverages provided through the National School Lunch, Breakfast, and Smart Snacks Programs, affecting fifty million children daily at 99,000 schools. The legislation's impact on childhood obesity is unknown. We tested whether the legislation was associated with reductions in child obesity risk over time using an interrupted time series design for 2003-18 among 173,013 youth in the National Survey of Children's Health. We found no significant association between the legislation and childhood obesity trends overall. For children in poverty, however, the risk of obesity declined substantially each year after the act's implementation, translating to a 47 percent reduction in obesity prevalence in 2018 from what would have been expected without the legislation. These results suggest that the Healthy, Hunger-Free Kids Act's science-based nutritional standards should be maintained to support healthy growth, especially among children living in poverty.