There's a food court-type area by Tower of Terror and Rockin' Roller Coaster. I forget what it's called, but you'd notice it if you walked by. There's a couple of different windows and lots of seating (much of it is covered, so you're out of the sun/rain). It's not really anything special, but we always end up eating there because it's conveniently located next to the major rides and because we usually find better variety there than at other fast food locations throughout the park. They sell hamburgers, personal pizzas, salad, turkey legs, french fries, and I think taco salad. Of course, they sell beverages here, and there's condiment stands, so if you need napkins/silverware/ketchup/etc, you're set. If you're going to bring food in, this might not be a bad place to eat it because there's lots of seating available.
If your kids have seen Toy Story, you might consider stopping by Pizza Planet. You said they are 4 and 2, so they might be a bit too young to make the connection between the movie and the restaraunt (In the movie, Andy takes Woody and Buzz to Pizza Planet). They sell (you guessed it) primarily pizza there. It's fast food as well. And, like in the movie, there's claw machines. There's also a variety of other arcade games, if memory serves. It can be a bit loud at times, but it's a fun atmosphere.
But, if you're bringing food in, your best bet is the spot by Tower of Terror. Lots of covered seating and a convenient location.
