Hi Jody,
Welcome to the Moms Panel! In my experience, just about everything at Walt Disney World is entertaining to little ones..but here are two of my favorite places to go for "free" entertainment:
Downtown Disney - We could easily spend the better part of a day here. There are lots of shops, and fun displays to browse. They have a small playground at the Lego Imagination Center (as well as lots of Legos on display to play with). The Once Upon a Toy Store is always a hit because they also have interactive displays where the children can do things such as build their own Mr. Potato heads, just for fun! There is an outdoor theater that has various entertainment, which is also free. If it's a warm day, be sure to bring a change of clothes so they can spend some time playing in the squirting fountains.
Disney's Boardwalk - This is a wonderful place for free evening entertainment. We really enjoy visiting this area for evening strolls. There are carnival type games and face painting (both for a fee), but on most nights there are street performers doing various acts of entertainment that is fun for all ages.
You should also check out your resort at
www.allearsnet.com to see if it has a playground, many of the Walt Disney World Resort have fantastic playgrounds which is a great way to spend some time.
Hope this helps!