The first time we took my daughter she was two, but very small for her age. She loved it all! She loved the teacups, Winnie the Pooh, Buzz Lightyear, the carosel (I know I spelled that wrong).
Don't think that they won't also enjoy Epcot or other things - my kids found things to look at and explore everywhere at Disneyworld! Just be sure and go at their pace. Also, my daughter was not so sure about characters. So, we didn't push it. Just waved if we saw one, and kept going.
They do like the parades!
Bring a daypack with a change of clothes for each of them in it, in addition to your usual diaper bag stuff. I used to use a backpack, and hang it on the stroller.
Bring you best double stroller. My kids both napped in ours.
Have fun planning!