PHILADELPHIA — One boy was killed and another wounded by gunfire as they were riding a dirt bike on a street in northeast Philadelphia, authorities said. Police said the 11-year-old and the 14-year-old were shot at about 6:30 p.m. Friday in the Oxford Circle neighborhood. The younger child was hit in the neck and was pronounced dead minutes later at St. Christopher’s Hospital for Children. His name wasn’t immediately released. The older child was shot in the arm and ankle and was in stable condition at Jeanes Campus at Temple University Hospital. Police said no one was immediately arrested and no weapon was recovered.