A report by the Centers for Disease Control and Prevention, published in the Journal of the American Medical Association, said obesity prevalence for this age group went from nearly 14 percent in 2003/2004 to more than 8 percent in 2011/2012 -- a decline of 43 percent.
The CDC used data from the National Health and Nutrition Examination Survey.
"We continue to see signs that, for some children in this country, the scales are tipping. This report comes on the heels of previous CDC data that found a significant decline in obesity prevalence among low-income children ages 2 to 4 participating in federal nutrition programs," Dr. Tom Frieden, director of the CDC, said in a statement.
"We've also seen signs from communities around the country with obesity prevention programs including Anchorage, Alaska; Philadelphia; New York; and Washington. This confirms that at least for kids, we can turn the tide and begin to reverse the obesity epidemic."
The precise reasons for the decline in obesity among children ages 2 to 5 are not clear, but many child care centers have started to improve their nutrition and physical activity standards over the past few years, Frieden said.
In addition, the CDC data showed decreases in consumption of sugar-sweetened beverages among youth in recent years, the study said.