GF baking is hard, man. Really, really hard. And a lot of it still tastes like shit even when you get it "right." Xanthan gum is definitely a critical ingredient though, you can't just omit it and hope for the best.
What kind of flour did you use? A blend that is high in tapioca starch is likely to be the most palatable to a kid.
Personally, if you're trying to keep a 7-year-old motivated, I'd let him have a commercial pre-made GF crust for now, and expand your repertoire later. Kinnikinnick is by far the best, IMHO. My non-GF family members openly like them. They make fantastic hamburger/hot dog buns too.