My daughter is 5 now and has been to WDW each year so far.
At MGM, my daughter loves Playhouse Disney, Little Mermaid, the Animation Tour, Muppet Vision 3D, Indiana Jones, Beauty and the Beast & Fantasmic. The parade is fun and full of characters, too.
At Epcot, she loved world showcase because we tried different foods at each country and she loved the Kidcot stations where she made her mask. She also really loves Spaceship Earth, The Living Seas, Imagination and Listen to the Land boat ride and Lion King movie in the land.