Another vote for
Animal Kingdom! 
Can you Park Hop?
The following are fun things at
MGM for young kids...
1) Beauty and the Beast (Broadway type musical)
2) Ariel
3) Muppetvision 4-D
4) PlayHouse Disney
5) Characters are in front of the Sorcerer's Hat for photos and autographs
6) Woodys Toy Barn (photo/autograph opportunity with Toy Story characters)
7) Honey I shrunk the Kids playground
8) Stars and motorcars parade
AT AK:
1) Dinoland has a Dumbo like ride called Triceratop spin
2) Dinoland also has a "cheesy" carnival area with fun games where kids can win a stuffed animal. (BTW, it is meant to be cheesy! and fun! lol)
3) Pocohantas has a cute show with animals.
4) Wonders of Asia Bird show
5) Kilamanjaro Safaris
6) Festival of the Lion King
7) The BoneYard playground
8) It's Tough to be a Bug can be scary for young children. Every show at least one parent is seen doing a quick exit stage left!
9) Mickey's Jammin' Jungle Parade (This is GREAT! Shades of Epcot's old Tapestry of Nations!)
Have a great time!