On the down side, obesity rates among lower-income children remain more stubbornly stable, researchers report in the journal Pediatrics.

Recent studies have shown that after decades of rising obesity rates among U.S. kids and teens, the numbers seem to be leveling off.

But less has been known about young children specifically, said Dr. Xiaozhong Wen, of Harvard Medical School and the Harvard Pilgrim Health Care Institute in Boston.

Patterns in that age group are important, Wen said, because they give a glimpse into the future of the national obesity problem.

So his team looked at obesity trends among kids younger than six who were seen at greater-Boston-area pediatric offices.

The researchers found that after holding steady between 1999 and 2003, the obesity rate began to fall after 2004.

By 2008, just under nine percent of boys were obese, compared with almost 11 percent between 1999 and 2004. Among girls, the obesity rate declined from over eight percent to just over six percent.

The trend was similar to what was going on nationwide at the time, the study found. But Massachusetts children had a lower obesity rate than the national norm, and the decline over time was sharper.

Based on federal health survey figures, just over 10 percent of two- to six-year-olds in the U.S. were obese in 2008. That was down from 14 percent in 2004.

The rate among children younger than two, though, stayed steady at 9.5 percent.

The findings raise the possibility that young children in eastern Massachusetts may be "leading a new wave of better weight status," according to Wen.

Or that at least may be true of young children with private insurance, he said.

"We didn't see much change in children on Medicaid, unfortunately," Wen told Reuters Health. Medicaid is the government health insurance program for the poor.

Of Massachusetts children on Medicaid, 11.5 percent were obese in 2008, which was down from just over 12 percent in 2004.

Wen's team found a similar trend in a national database that tracks mostly low-income U.S. children. There, the obesity rate remained stable between 2004 and 2008 -- at almost 15 percent among children between the ages of two and six.

It's not clear why obesity was generally less prevalent among Massachusetts kids versus the nation as a whole, Wen said.

But one reason, he noted, could be the higher percentage of Asian-American children in the Massachusetts study group. In addition, families in the state sample may have been higher-income versus the national average.

Wen said he could not say for sure why obesity is declining among young children in Massachusetts, and possibly nationwide as well.

He speculated, though, that greater awareness of the problem and pediatric screening for obesity could be playing a role.

Wen also noted that smoking during pregnancy, which has been linked with an increased risk of childhood obesity, has declined. At the same time, breastfeeding -- which is associated with lower obesity risk in kids -- has become more common.

Those are all potential factors, agreed Bettylou Sherry, a researcher at the U.S. Centers for Disease Control and Prevention (CDC) who also worked on the study.

Another is the fact that birth weights nationwide have "unexpectedly" declined since 2000, Sherry told Reuters Health in an email.

Some studies, but not all, have linked birth weight to obesity later in life.

Nonetheless, the rate of obesity among two- to 19-year-olds nationwide has held steady since 2000, hovering around 17 percent, according to the CDC. That came after 20 years of rapidly rising rates.

Wen said it will be important to figure out why obesity among young children -- at least the privately insured -- may be waning. Knowing what measures are working "will help us use our health resources more efficiently," he said.

Just as important will be figuring out why lower-income kids are not showing much, if any, improvement.

"This study raises the possibility that the socioeconomic disparity is widening," Wen said. "That's our concern."

For parents, he said the important thing is to realize that obesity prevention at a young age is "critical."

"Obesity is not an easy thing to manage at a later age," Wen said.

In general, experts recommend limiting kids' time in front of the TV and computer, and giving them plenty of "whole foods" -- like fruits and vegetables, low-fat dairy and fiber-rich grains -- instead of sugar-, salt- and fat-laden processed foods.

Wen said it's also important for parents to be "good role models" -- exercising and eating their own fruits and vegetables, if they want their kids to do the same.

SOURCE: bit.ly/I5siTe Pediatrics, online April 23, 2012.

• A Permanent Economic Emergency