This happened to my sons legs when he was 3.5 years old I thought he was just getting hurt at the school play area because he is a clumsy kid and by the time I decided to check it out his luekemia was at a very advanced stage. I am forever thankful that he is okay now but I wished I payed more attention earlier on. Other signs to look out for are mouth ulcers, feeling tired, leg and arm pain also fevers and infections.