The prevalence of obesity in U.S children has quadrupled over the past 25 years. A new study shows that TV commercials may be a culprit. The report revealed that junk food ads have a definite impact on what kids eat.

Food commercials aimed at children greatly influence what they choose to eat. That's the word from a new study by a group of scientists with the Institute of Medicine. Michael McGinnis says advertising sways children in several ways.

"It influences their preferences, it influences their request of parents, it influences their short term consumption patterns."

Last year, the food industry spent $10 billion on advertising for kids. Most of the commercials aimed at children advertise foods with little or no nutritional value such as sugared cereals, soda and fast-food meals. The ads feature popular cartoon characters, which entice children more. The study says the food industry should shift its advertising to promoting healthier eating habits. The food industry says it's already doing that.

Richard Martin is with the Grocery Manufacturers Association. He says that companies recognize profit in healthier food products.

"At the end of the day, healthy foods bring healthy profits and companies realize that. I think the fact that 98 percent of major food and beverage manufacturers are producing healthier products speaks for itself."

And there have been changes. Cartoon character Spongebob Square Pants is now promoting spinach and Blues Clues can be seen on milk cartons. However, the panel said the growth of new food products targeting kids increased from 52 in 1994 to almost 500 new products last year.

Some nutritionists say the industry must be regulated. The report called for the government to monitor food marketing over the next two years and if companies don't significantly change how they market food to children, Congress should then intervene.

One parent says that she's ultimately responsible for what her children eat. "They can cry all they want but it's up to me whether I buy it for them or don't buy it for them."

And kids aren't bombarded by TV commercials only. The scientists say images in computer games also expose children to junk food. And advertisers are using coupons, in-store events and even organized word of mouth campaigns to get children to get their parents to buy the products.