Hi, I can understand your concern for the red circular rash on back and leg in your son. There can be multiple possibilities of the problem and without pictures it is practically not possible to guide you for exact cause or diagnosis. I can make a possibility of allergic dermatitis due to sweating or clothes or friction. The only precaution you must follow is not to touch, pinch pop or squeeze any of them other wise it can get infected and can cause complications. You can start application hydrocortisone cream and Benadryl to help him out. Take care.