Glutenfreedish.com lists restaurants recommended by coeliacs! We will always have to quiz them regardless! Have you looked into dairy or oats with regards your son? Gf oats are a problem for around 5% of coeliacs and dairy/gf oats can be excluded and reintroduced slowly to see if it has an effect. If your son is a silent coeliac, he could well be getting glutened somehow. Keep a food diary and be sure to only use certified gf products.