Obesity is a big concern among US children, with nearly one-third of them either overweight or obese.

Junk food marketing is a contributory factor to such problems, according to the Washington-based Institute of Medicine.

Now, Walt Disney, one of the world's largest mass media companies, has decided to join the fight against obesity.

The company, known for its popular theme parks, plans to ban commercials for junk food on its widely watched children network Disney TV, radio, web channels - and inside the theme parks themselves.

Al Jazeera's John Terrett reports from Washington.