Obesity rates fell among U.S. 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 kids.

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

Researchers attributed the decline to greater awareness of health problems caused by obesity as well as an increase in breastfeeding, which studies have shown can reduce the risk. Obesity even at such a young age can set up children for diabetes, heart disease and even premature death, said Heidi Blanck, a study author.

“We’ve flipped from going up to really now showing a decrease,” Blanck, acting director of the Division of Nutrition, Physical Activity and Obesity at the Atlanta-based CDC, said in an interview. “It’s a modest decrease, but at least we’ve changed the direction. We’re optimistic that with recent investments and recent initiatives we’ll continue to see these numbers decline.”

Researchers used data from the Pediatric Nutrition Surveillance System, which includes about 50 percent of children eligible for U.S.-funded maternal and child health and nutrition programs. The study included 27.5 million 2- to 4-year-olds from 30 states and the District of Columbia.

The children were considered obese if their body mass index, a measure of height and weight, was at or above the 95th percentile for kids of the same age and gender, and extreme obesity was defined as having a body mass index at or above 120 percent of the 95th percentile. That means, a 3-year-old boy of average height who weighs 37 pounds or more would be considered obese, and a 3-year-old boy of average height who weighs 44 pounds or more would be extremely obese.