There is a possibility that your son could have "encopresis". Has he ever been constipated? Backed up stool can distend the bowel and liquid stool leaks around the large mass of backed up stool and results in soiling. The backed up stool can push on the bladder and cause wetting as well. Ask your doctor to check his belly. Your doctor may also do an x-ray of his belly or a rectal exam.