Actually, you could sail on the Navigator of the Seas and never spend a penny and have a fabulous experience. There are numerous dining venues that are included in your cruise fare. If your kids are looking for burgers and fries, they can have all they want at the poolside grill. The specialty restaurants (Chops, Portofino and Johnny Rockets) are simply extras that pwoplw can elect to visit for a unique dining experience, if they choose to do so.
You will have a great cruise.