Sorry to hear about your son, and I admire you for your support for him (You don't mention his age, or where you call 'home')
As far as food-based 'treatment' is concerned, I don't think there is such a thing, as every Crohnnie each has their own unique and personal dietary problems,
Most of us here will probably suggest, all you can do is the 'trial and error' method of eating, i.e. start off with limiting diet to ONLY foods you know do not cause pain/problems or upsets. once the gut has settled down a little, introduce just one new food to the menu, and keep a diary of everything that is eaten throughout the day, with comments about 'after effects' (whether they be negative or positive) e.g. flatulence, loose stools, stomach cramps, even if it exits the 'other end' in the same condition as it entered !!!(sorry to be over graphic but... needs must etc)
A general rule of thumb is a low fibre (low residue) diet, which means NO to foods that contain seeds, pips, grains, nuts, skins, whole spices, raw vegetables, raw or dried fruits, pop-corn. cereals, pulses, beans and peas.
Other foods that can cause upset, (variable in every crohnnie so here comes the trial and error bit)
dairy products, red meat, fats, and spicy foods.
I'm sure others here can add to the lists, and their own suggestion and experiences with controling their symptoms.
I hope some of this will help a little
Good luck to you and your son, do keep in touch to update us with his progress.