Hi, my daughter (12) is coeliac. She had a positive blood test after symptoms at about 6yo and an endoscopy a couple of weeks ago. (it doesnt usually take that long, it was our choice) It is a big shock initially, and you do feel guilty, like you are at fault somehow, and incredibly sorry for your poor child, but seriously, it isnt the end of the world. It does involve some small changes, but otherwise has little effect, IMO. And once they get onto a GF diet, (and you must wait until after any tests needed) they perk up very quickly.
My advice is to cook everything from scratch, and learn which things to substitute in your favourite recipes. (Polenta makes a good coating for fish fingers or chicken nuggets, which can then be shallow/deep fried, we all fight over those!)
Register with Glutafin, who are the company that provide a lot of the free prescription foods, they are fab. DD was sent a selection of sample foods in a nice 'hamper' which made her day, and the sent her regular mailshots and samples, including some lovely recipe cards.
The only issues she really has, are parties and eating out. Unfortunately, you cant make other parents provide GF food at parties, it really just depends on their individual characters, and restaurants are the same really, but with experience, you will know what to look for on a menu. (Mcdonalds are actually very useful for outings, their food is very uniformly made, and their paper tray liners have a full nutritional breakdown on the reverse, including salt, dairy, nut and gluten. I always find that if I take a gluten free bap with me, they will pop their burger inside happily)
My whole family eat GF now, and rarely notice the difference. There is obviously non GF bread available, but most other stuff is no different or even sometimes better. This will also help you to avoid cross contamination, which, if someone is very sensitive, can be an issue.
Please dont beat yourself up over this though. In a very short time, you will have your head round this, and it will be such a small part of life that you will barely notice! Before DD was diagnosed,she was so poorly, I seriously thought she had leukaemia or something equally as horrible. Just think how much worse THAT would be. When I remember how worried I was, I thank my lucky stars that she only has coeliac disease!
Please, feel free to PM me if you need to talk some more, Im happy to help. xx