LOL, well, I'm sure the Disney-police will jump in immediately to say it's "O'hana"; some people have a big pet peeve about that, hehe.
Seriously, though, I don't think you will have an issue. The food is pretty "basic" so most kids do well with it, but if they don't the Kona Cafe is right next door and they will bring you things from the kids menu there if you need (french fries, chicken strips, etc.).
O'hana is a wonderful place, and you can be sure that if your son really doesn't like the family-style food, the waitstaff will be more than happy to find something he'll like.
Good luck!
AEfx