ANN ARBOR, Mich. - There's no harm in allowing kids a few extra cookies, a box of candy canes, some fudge and an extra helping of turkey and mashed potatoes during the holidays, right?

For some kids, a few extra treats in moderation during the holiday season is harmless. But for others who indulge year-round and get little exercise, extra holiday indulgences only add to weight gain and the prevalence of childhood obesity in the United States.

The problem, say researchers at University of Michigan C.S. Mott Children's Hospital, is that large numbers of parents fail to recognize that their children are overweight or obese, and therefore may be less inclined to modify their children's diet and activity levels.

According to a new report by the C.S. Mott Children's Hospital National Poll on Children's Health, more than 40 percent of parents with obese children ages 6 to 11 describe their child not as obese, but as "about the right weight."

In fact, the report finds only 13 percent of parents with obese children ages 6 to 11 rate their child as being very overweight, compared with 31 percent of parents with obese children ages 12 to 17. And, less than 10 percent of parents with obese children ages 6-11 say they are "very concerned" about their child's weight.

While most parents agree childhood obesity is a major health issue, many underestimate their own children's weight and fail to take corrective steps to manage weight gain. Without intervention, childhood obesity can take a hefty toll on a person's life-long health.

"It is critical to address obesity in the childhood years - at home, and in schools and other community settings," says Matthew M. Davis, M.D., M.A.P.P., director of the National Poll on Children's Health. "But in order to address childhood obesity at home, parents must first recognize that a child is not at a healthy weight for their height. Parents also must be concerned enough to want to do something about their children's obesity."

One of the greatest challenges for parents is that children's obesity may not be easy to judge subjectively, he says. Obesity is based on a child's body mass index, or BMI. When a child's BMI is at or higher than the 95th percentile for children who are the same age and gender, the child is obese. For example, a 6-year-old boy who is average height (3'91/2'') would be considered obese if he weighs 55 lbs. or more.

Based on results from the latest report from the National Poll on Children's Health, Davis says parents may under-estimate their children's weight, and/or over-estimate their children's height. Parent-reported height and weight for the poll indicate that 15 percent of children ages 6 to 11, and 10 percent of children ages 12 to 17, are obese. Overall, 25 percent of children in 2007 were reported as being either obese or overweight.

These parent-reported estimates, however, fall short of previous data on childhood obesity and overweight obtained through national studies. The studies - in which children's height and weight were measured in person - found that 35 percent of U.S. children ages 6 to 17 are obese or overweight

Even with this underestimate, Davis says there is a stark mismatch between children's obesity and parents' perception of whether their children's weight is appropriate.