BB has Tike's Peak, an area especially for preschool age kids. The MAX height to play there is 48". My DD is 7, but only 46"- she did a few things, but liked the area for older kids better. For 5 and 2 year olds, though, it should be perfect.
As for other things to do, most little kids say their favorite thing about a Disney vacation is swimmimg in the pool at the hotel. Give them lots of pool time, and they'll be happy!
There are some fun evening activities at Fort Wilderness for guests of the Disney Resorts. Chip and Dale have a campfire each night with singing and storytelling (and it's FREE), then afterwards they show a classic Disney movie outdoors on a big screen. It's lots of fun. There are also horse and buggy rides there. During the day, FW has a cute little petting zoo area, and the horse barn where you can go see the pretty horses who work at Disney, pulling the Main St Trolley and other things.
Downtown Disney is fun for little kids- there is the
Lego store- it has outdoor Lego tables where they can build stuff, and a play Lego house and play area. Goofy's Candy Co is neat to visit, and World of Disney is great for shopping. There is also a store called (I think) Disney Emporium- they sell things for as little as $1 up to $10 there.
There are a couple of mini-golf courses, too- they would be fun for your little ones.
There are lots of non-park things to do with preschool age kids- I'm sure there are lots more that I haven't thought of. Read up on the DIS, Allears.net, and the UOG and Passporter. Have fun!