Last year, when my daughter was 3.5, we went to Florida for 2 weeks. She had no previous experience of theme parks at all.
We started at IOA and my daughters very first ride was the Cat in the Hat - she absolutely hated this, and wouldn't go on another ride all day, in fact even a few days later she was still spooked, however, when we got to Disney I managed to convince her to try It's a Small World (and it was tough to get her on there) and she really liked this - we did a day of really easy rides, Pooh was about the scariest thing we tried, and slowly she got a little braver. She quite liked the Lion King show at MK. She also LOVED Belles storytime - this was one of the best things we did.
Epcot: She liked Spaceship Earth, and was ok with Imagination on our last day (but would have hated it earlier in the trip). She also liked The Land, and the Norway ride (but wasn't too keen on the Troll). In fact, I think she was fine for most of Epcot, we didn't take her on Ellen's Energy Adventure, but other than that we didn't do any swapping and she came with us on everything. (We didn't do Test Track, HISTA or Body Wars)
At MGM she was OK with Muppets 3-D, but we sat near the door just in case, and also managed the Little Mermaid (although she wasn't too happy about Ursula), and was quite happy in Backstage Pass, and Who wants to be a Millionaire (in fact she still talks about that), her favorite was Bear in the Big Blue House.
AK - she was fine on the Safari - loved the Pocohontas show and the Lion King show (this was a highlight) and was quite happy walking though the animal walks.
Katie was really really nervous of rides, and a couple of things that helped were getting a light-up Pooh bear which we took into all the dark rides ( this was a big help), and also having Katie asked the CM at the entrance to each ride if it was scary, and what would happen.
All the CM's at Disney were lovely and quite happy to explain to Katie exactly what might happen, this was how she ended up doing the Imagination ride, after the CM explained that it would be dark and you would be able to hear a train coming, I asked Katie if she still wanted to go on, and she said 'that will be ok mummy, Pooh will make it light for me' and she was perfectly fine. (I however jumped out of my skin at one point!)
We did encounter one CM at Universal who was a bit hopeless - we asked her if the HannaBarbara ride was scary, and she said No - it;s just cartoon characters , so in we went, and we sat at the front in the non-moving seats. Well, after about 2 seconds we had to come out as she was absolutely terrifed. It was very fast (the image) and loud, and she was still quite nervous from Cat in the Hat and she just didn't like it at all.
if you want to read my trip report, I tried to describe which rides we found to be ok and which were too scary.
It's here.
My trip report
Bev