Daniel Moore was battered about the head with bricks, broken bottles and pieces of wood in a playground near his home on the Edgar Road estate in Hounslow, west London.
Witnesses said the attack on Tuesday night was mounted by mainly Asian youths. Daniel is white, but police were last night playing down a racial motive.
He was taken to Great Ormond Street Children's Hospital where surgeons earlier today operated on a fractured skull.
His father, Pc Dale Moore, is based at the local Hounslow police station.