Also, is it fun and appropriate for a 2 and 4 year old?
There is not a WHOLE lot for children this age to do, but that didn't stop my barely 3yr old at the time from being the one we had the most trouble getting to leave there. LOL
She liked the things on the level where they do the character drawing lessons and music stuff- in the center there they have drawing things that are really neat... she was there for hours (even though she was too short and they didn't have enough of the blocks to stand on for her to be high enough- all the kids had to use those and we had to hold her up on our knee the entire time! We took turns LOL)... and she also liked the midway area (which does cost) to play games and get tickets and use them to buy stuffed animals and little trinkets. That was right up her alley. LOL But really the drawing stuff is what took her attention the entire time there.
If you can split up- you should be able to find things for all ages. Ours were 8, barely turned 6, and barely turned 3 at the time and they all had things they enjoyed and had a blast. But if you can't split up (ie: one parent or some other reason) it's going to be difficult- they aren't going to like the same things and the 2/4yr olds aren't going to like standing in line for virtual simulation games and such. I think you would probably do fine with your oldest off doing her own thing while you are with the youngest doing what they like.
Oh to answer your question- even for the top floor midway type games (to get tickets to use to buy trinkets) you don't need to bring quarters- they have a desk there that you can get change (from cash, credit card, etc.) if you want to. So there's no need, even for the few things that do cost, to have to bring quarters with you.
