Sorry to hear about your son. My son also has Crohn's disease, although he was 11 when he was diagnosed. I just wanted to give you the website address for the Dragonpack site that was mentioned. There are parents on there with very young children also who can help you with what you are going through.
I would really like to hear from people as to what has worked for their children. My child just turned eleven and we waited almost 2 years for a proper diagnosis of Chron's. He is currently on pentassa, imuran, coulterelle, and prednisone. He is also taking fortified shakes to try to gain weight. Problem is that they are talking about discontinuing the imuran because he is still having pain when off the prednisone. They are talking about Remicade. Anyone have a child that has been on remicade? If so, side effects, etc would be helpful to know about!