Hi, L.. Have you checked with the doctor about this problem? I have a little girl in my care who does this. She is almost 5, and her doctor recommended having her practice stopping and starting when she is going to the bathroom. It will strengthen those muscles in case they are a little weak. He may be rushing to get done, and not get it all out. You might go in the bathroom with him and make sure he is finishing. I would stay as patient and calm as you can, as any stress in this situation can compound the problem. Good Luck!