Concern has been mounting about childhood obesity for the last 30 years. Approximately 17 percent of American children ages 2-19 are obese according to data from the Centers for Disease Control and Prevention.

As the numbers inch upward, obesity has become part of the national conversation, with aggressive advertising campaigns in major cities and a push by Michelle Obama to encourage kids to eat healthier foods and get exercise through sports and outdoor play.

New data suggests these efforts are paying off. New numbers from the Robert Wood Johnson Foundation show that in Philadelphia, New York City, Mississippi and California, childhood obesity is actually declining.