Most children have heard their parents shout “Sit up straight!” or “Don't hang your head!” when they eat dinner or do homework. Now such shouts often happen because of another activity——video games. Ten-year-old Tom says it takes him three to four hours a day to play games on his computer. And he plays for about two hours on the smart phone every day. As a result, he began feeling a serious pain in his neck two months ago. What’s worse, the pain has spread to the hand and back, which makes his mother worried.The doctors say the number of young children with this kind of pain in t