We just returned a few days ago with DD who turned 5 and DD 17 months old. She did really, really well, and we didn't know what to expect from her! We ended up having her as a lap baby, but DH and I both agree that in the future, she will have her own seat. She didn't fuss too badly, but she likes to have her freedom. As soon as we could, we had her run up and down the aisles a few times. We brought lots of toys and books to keep her busy, and she liked looking at the TV (we were on Jet Blue.) She did fall asleep a bit both ways which helped tremendously. So, it wasn't too bad, but she did get heavy!
So far as rides and attractions, she didn't get scared or fussy on anything we took her on! She loved the parades, light parade, and fireworks too. And she was fascinated by all of the characters we met, especially the face characters. We thought she might be scared of them - but she just wanted to touch their noses and give them kisses! We were also grateful for play areas, as she just wanted to run around most of the time.
Magic Kingdom--
Pooh's Playful Spot playground - she loved this, especially the slide
Winnie the Pooh ride
Peter Pan
Cinderella's carousel
Dumbo
Aladdin
Country Bears - loved this one!
It's a Small World ** did this FOUR timess - she pointed at eveything and was so cute!
Buzz Lightyear was fine
Pirates was OK too
she also loved Mickey's Philharmagic
this all depends on your child, of course!