We took our 2yr 8mo old dd in October and had a blast. I'd suggest starting off with the rides you think she'll like the best. We made this mistake with our older dd when she was little, by taking her on Mr Toad (at DL) first. Well, we had forgotten how dark that ride is, and she was scared of the dark, so she was scared to even try anything else. expecting them all to be just as dark. So, with our second dd, we made sure to go on Small World, Winnie the Pooh, etc, first, so that if any ride scared her, she would at least know that not all rides are scary.
She didn't like Pooh, because the Heffalumps and Woozles part was "too scary". She didn't like Peter Pan or Pirates, because they were too dark. We didn't even think of taking her on Snow White, HM or Maelstrom, they would have been way too scary for her. She loved Dumbo, Goofy's Barnstormer, Alladin's Magic Carpets, Jungle Cruise, TTA, Speedway, Astro Orbiter, the Train, Triceratops Spin, Kilimanjaro Safari, HISTK playground, Pooh's playground, El Rio del Tiempo, hmm, I'm sure there was more, but I'm drawing a blank.
The one thing that was a bummer was that she was too short for several rides I know she would have loved, like Soarin', BTMRR, Splash and Primevil Whirl. She kept watching the logs come down at Splash and was very upset that she couldn't ride it.
We had planned to go back to the hotel for naps, but once we were at the parks, we were having too much fun and no one wanted to leave. dd2 just napped in the stroller. She's always been pretty good about doing so, but it was even easier for her at DW, since she was tired from all the excitement. We found a great place to stroll her to sleep at MK, it's in
this post, if you want to take a look.
She also loved the water parks. She was happy just digging in the sand, and also loved the lazy rivers, the family raft rides, and the kiddie slides and play areas.
Characters... We also watched videos like DL Fun (mentioned above) and the planning DVD, to get her used to what the characters look like, and how big they are. We made sure she knew they are "as big as mommy and daddy", since they can be overwhelming sometimes for little kids. We also made sure she saw the Looney Tunes characters at our local Six Flags park, just to get used to them before Disney, too. Some kids just don't like characters, and that's OK, too. My 8yo still would rather not be near them, but the 2yo loves them, and was very into getting their autographs. She especially loved the princesses and going in the castle.
2 is such a fun age at Disney. Have a great trip!