Children has gained 65 percent more fat around their bellies, among boys, and almost 70 percent among girls between 1988 and 2004.

Abdominal obesity is dangerous in any age, especially in children, becaues it predicts very high chances for cardiovascular disease and type 2 diabetes risk.

Belly fat is becoming a more reliable sign of future health problems, as Body Mass Index, a weight to height ratio, can sometimes be misleading. For example, a child may not register a very high BMI score, but if he carries a lot of fat around his middle, he may be at a higher risk for health problems than other children with the same BMI score.

The first nationally representative study to document the increase in children's belly fat, the study in today's Pediatrics paints a bleak picture for these children who have a higher risk of heart disease, adult-onset diabetes and metabolic syndrome.

The good news is that, for children and teenagers, improved lifestyle for weight loss is often easier to adopt.

"Kids, teens and adults who have early stages of atherosclerosis in their arteries can have a healthy cardiovascular system again," said Stephen Cook, M.D., an assistant professor of Pediatrics at the University of Rochester Medical Center's Golisano Children's Hospital at Strong and an author of the study about childhood abdominal obesity.

"Older adults who have plaque build up have a much harder battle, especially if the plaque has calcified."

Cook said there is no gold standard yet for how waist circumference should be measured and no consensus yet on the cut-off point for abdominal obesity.

However, he added, the study should be a warning for physicians and parents to limit sedentary activities, such as TV and computer time.

Childhood obesity is a serious and growing problem - perhaps even more than people already believe.

According to data from the National Health and Nutrition Examination Survey (NHANES) between 1999 and 2004, the percentage of 6- to 11 year-old children with high BMI scores rose about 25 percent (15.1 percent in 1999-2000 to 18.8 percent in 2003-04).

But the increase in abdominal obesity of the same group over the same period was even more dramatic, more than 35 percent (14.2 percent in 1999-2000 to 19.2 percent in 2003-04).