The MBTA Transit Police said a 12-year-old boy was injured in a fall while trying to "train surf." Shortly before 1 a.m. Tuesday, the child tried to ride atop a Red Line train car that originated from the JFK-UMass stop in Boston's Dorchester neighborhood, authorities said. WATCH HERE WATCH HEREHe suffered a serious but non-life-threatening head injury. Transit police said they hope the child makes a full recovery, but warned the public about "the inherent extreme danger of 'Train Surfing.'" "It could literally cost you your life," MBTA Transit Police Superintendent Richard Sullivan said in a statement.