Hi December's flower. Newest research indicate Crohn's is not a classical autoimmune diesase (like Hashimoto's, where you can find antibodies against the body's own cells). Rather it's an immunodeficiendy, where the body responds inadequately to something. NOD2 and CARD16 as well as other genes seem to be involved, meaning that there is some genetic predisposition to the disease. But it seems there has to be one or more trigger(s).
The way I like to think about it is: some people will get the flu during winter, some won't. It comes down to how their immune system is wired as well as whether they are exposed to the virus.
So what seems to be current consensus is that your child may or may not be predisposed, but the disease will only break out if... which is where things start to be vague in the litterature: Bacterial infection? yeast infection? both? Certain foods?... I wish I knew.
Anyway, I think we need to err on the side of caution and set an example to our kids to stay clear of milk products (mycobacterium paratuberculosis exposure), gluten (molecular mimicry), and too much alcohol (gut bacteria destruction etc.)
hope this is will be food for thought - pun intended