T.S.
You may wish to talk to a dietary person as well. My daughter is vegetarian and we did this and it did really help us; Soy Milk may be an option and avoiding processed foods (certainly with nuts, milk, eggs). I would check organic things out (go to Trader Joes or Woodmans or Dominicks has somethings as well), like the cheeses or other things to see how they process if you want your son to eat it. Good luck!
T.