Admission covers cost of most.
There is an arcade section you can pay to play because you get tickets to turn in for prizes. We usually skip.
Also activities that you can choose to purchase such as designing your own toy (Sid of Toy Story style) and then they will put together a kit and you buy, or make a cd or buy a copy of art you did in cartoon class or purchase video of you riding your virtual roller coaster. (you can still do all of these things without purchasing end result)
Design a coaster then ride it in a simulator, virtual pirate ship battle for gold (really cool), virtual aladdin magic carpet ride, virtual (although you are on a real raft with oars) jungle raft ride, buzz lightyear bumper cars with nerf balls, lots and lots of arcade games, be a pinball in a pin machine, virtual dualing it out with cartoon villians, virtual space pod trying to fight and gather settlers.
The 2 and 4 may get alittle overwhelmed depending on their personality. Older kids will LOVE it ! We planned to spend 3-4 hrs our first time and ended up in there for 8. Food inside is reasonable and good.