my son has had bruising on his spine about four or five times since he turned one, he turned two last week. normally there is only one or two bruises at a time, once there were three bruises. and i only really am getting worried because he had one a week or so ago and last night had two (they have never been so close in proximity when he got them). there is nothing i can figure out that is causing them either. what could this be from? and should i be worried?