Maybe one of the moderators can move this to the Natural Treatments forum. I think most of us over there will see it here, too, though.
What kind of food did you order online? I order pretzels, flour, and some cake mixes online. Stores like Whole Foods and some health food stores will have it, too. Even regular grocery stores are starting to have the gluten free items but not as large of a selection.
Here is a list of common grocery store items that you can eat.
http://www.dallasrock.org/pdf/ManyThingsToEatRightNow.pdf It is several years old so you need to read the ingredients before you buy anything but it will be a starting point.
My children and I are all on the gluten free (and casein free) diet. Since I also eat it, I know that most of what you buy ready-made is not very good. I would start your child on naturally gluten free foods first and let him try the gluten free substitute foods once you know if you are going to continue it. If he tries some of that food, he will more than likely be turned off from the whole thing. You really need his cooperation to do it. I will tell you a really good brownie mix is the Gluten Free Pantry brownie truffle mix. Before I needed to be gluten free myself, I compared it to a regular brownie mix and it was much better!
Naturally gluten free foods are whole, unprocessed foods. Regular cuts of meat that you season yourself, cheese, eggs, a lot of yogurts, fruits, vegetables, rice (not preseasoned mixes usually), potatoes.
It would be worth your time to go to
www.glutenfreeforum.com and search on foods to see what most people like. It will save you from a lot of bad pre-made gluten free substitute foods. You can also read many tips on how to start the diet and stories from people who have noticed dramatic improvements in their kids or themselves for inspiration.