cooksters my daughter did that when she was 18 months old but we didnt know there was anything wrong with it until six weeks later when a lump came up. She was alwas so good and happy you would never have known. But anyway the lump did go down after time. Becuase she was so young and her bones where soft maybe that was why. How old is your son.? Could be the lump stays if they are older. Thinking about that I know a man who still has a lump from last year when he broke his. But it is not a bother to him. wish him well from me. Brenda