Sorry to hear about your son's diagnosis. My son (now 15) was also diagnosed with Crohn's at age 11. I just wanted to let you know of a terrific support group for parents of kids with IBD. These parents have all been there, done that, and could offer you a lot of advice on traveling with your son. The site is dragonpack.com/ibdsupport/parents/
(I am unable to post a link, but hopefully you can figure out the address)
By the way, we have made many trips with my son and it hasn't been an issue. If your son is not flaring and knows which foods he should stay away from, you should be fine. As dvccruiser76 said, make sure you know where the bathrooms are. My son is in remission and I still do this when we go anywhere.