I've had crohns for over 23 years, in fact I just had 2 feet of my intestine removed 12 days ago. I'm sorry for you and your son to have to deal with this crummy disease, it's a real curse. Speaking for myself one of the most frustrating aspects of it, especially in the beginning, was trying to pattern what aggreed with me & what didn't. This led to extremely erratic bowel movements and the way I felt overall.
I guess my advice would be to keep track somehow of what Ko eats along with bowel movements and overall feelings. The big thing to remember is that even when he's feeling good, his bowel movements will most likely be erratic.
Hope this helps and good luck to both you and your son.
Mike