BAKERSFIELD, Calif. -- American children spend an average of six hours per day watching television, using the computer and playing video games. That's more time than they spend on reading and writing in school.

Doctors have said that parents don't realize the effects that popular media can have on children and teenagers.

A paper published in the Journal of the American Medical Association noted that increased media time among children has been linked to a greater chance of obesity, smoking, violent behavior and eating disorders.

Experts agreed that media use can be helpful to kids -- educational programs can teach children about science or animal life, and the internet is a valuable research tool.

But kids are getting too much unsupervised "screen time," doctors warned. Many children have televisions, computers and cell phones in their bedrooms.

The American Academy of Pediatrics urged parents to limit kids' media use to two hours per day -- and to discuss the content of programs and games with their children so that the media messages are balanced by thoughtful parental guidance.