Children who play computer games and use cell phones for long periods are at risk of serious wrist and finger pains, according to U.S. experts.

Health warnings and age limits on games should be considered because consoles and smartphones could be harming tendons and joints, Professor Yusuf Yazici, of New York University Hospital for Joint Diseases, will tell a conference Wednesday.

The guidance comes after what Yazici believes is the first study of the effects of gaming on children's wrists and fingers. When the 12-year-old son of a colleague complained of problems, Yazici and his researchers studied 257 gamers, aged between nine and 15, in two schools in St. Louis, Missouri.

"The average was about two hours a day and 25 percent of them reported pain," Yazici said. "The younger the kids were, the more pain they had. The more they use [consoles], the more pain they had—an extra hour of play doubled the odds of experiencing pain."

Parents should monitor the amount of time their children spend playing computer games and using their phones, Yazici will tell the annual congress of the European League Against Rheumatism in London.

"Kids do not have a fully developed musculoskeletal system," he said. "At nine years old you're still growing. These devices are not designed for people with weaker hands and tendons."