The Scarlet Boy by Arthur Calder-Marshall 1961, paperback
Back cover: Charles Scarlet, with his strange blue eyes set in an olive-complexioned face, was always an odd boy. Even the games he played were vicious and somehow evil. He was ten years old when he died in mysterious circumstances. But although he was dead, his evil lived on, encroaching on the lives and happiness of all who came, strangely, unwillingly, nto contact with the Scarlet boy.