K.M.
Does he have an exersaucer or jumping toy he can still go in? Most kids his age have out grown them but seeing he is so far behind physically, it may still work for him. They are great for developing leg and trunk muscles. A friend of mine whose son had constipation issues would feed him foods that are supposed to help things along and then a little while later put him in his exersaucer. She swore it worked like charm!