By Susan Heavey WASHINGTON (Reuters) - Many young athletes still do not admit when they have suffered a head injury despite increased awareness about the risks of concussions in children and teenagers, U.S. health advisers said on Wednesday, urging sports leagues and government agencies to take more action. Various groups have tried to raise awareness about the seriousness of brain injuries, and sports leagues have implemented rule changes aimed at preventing them. Professional leagues, including the National Football League, are also wrestling with the issue amid complaints from some players about long-term impacts on the brain. But there is still not enough data on how to prevent and treat them, the experts said in an analysis of sports-related concussions in young athletes from the Institute of Medicine and the National Research Council. Click here to read full news..