NEW YORK ­— Obesity rates fell among US preschool-age children in 2010, reversing a trend of the past decade, according to the first national study to spot a decline in the condition among young children.

The rate of obese 2- to 4-year-olds from low-income families dropped 1.8 percent in 2010 from 2003, while it fell 6.8 percent for those who were extremely obese, the US Centers for Disease Control and Prevention reported in a research letter published Tuesday in the Journal of the American Medical Association.