I'm sooooo sorry he's having a rough time...
jmho.....give him lactobacillus acidophilus for a while. I would not start out with VSL#3. VSL contains several strains of Bifido bacterium which Gottschall concluded after extensive research was NOT GOOD for Crohn's and UC.
BUT MOST IMPORTANT: The "sachets" or packets of VSL#3 have CORNSTARCH as a filler!!! This is NOT good for anyone with Crohn's. Here is a link that lists cornstarch as a filler in VSL. Scroll down to "Product Specifications":
When I used VSL#3 for my son, I only purchased the capsules, which do NOT have cornstarch. We had very good results with the product, but we ONLY used the capsules. Cornstarch is evil.
Also, immediately after his diagnosis we started him on a different brand of probiotic. He did not take VSL until at least a year later--maybe 2 yrs later, I can't remember.
Remember, if you want to purchase lactobacillus acidophilus capsules for your son and he cannot yet swallow capsules, you can always break them
open and stir them into yogurt or something else.
Oh, and I think Roni's suggestion of a probiotic especially made for children--like Udo's--is a GREAT suggestion!