The signature pizza at Mythos varies from day to day - it is not a plain cheese pizza with optional toppings, if that's what you mean by regular pizza, though you can get a personal-sized plain cheese pizza on the children's menu. My son, also a picky eater, likes both the kid pizza and chicken fingers on the Mythos kid menu.
In terms of reservations at CityWalk, you can reserve some of the restaurants at the dining kiosks at the parks. There is also a reservations kiosk on CityWalk itself (at the bottom of the escalator when you come off the parking garage - near Pastamore's). Last week we tried to reserve NBA City at 7:30 PM and were told that was too early - they only accept walk-ins then. I don't know what the rules are during the summer, though.