We were just there for the conference with a 18mo, 4, 6 and 7yo. Magic Kingdom was the clear winner.
April shouldn't be too bad. We were there the last week in June and it was 37-38c with 100% humidity every single day.
The nice thing about Magic Kingdom is that they have loads of shows. We walked through all the shops to get around, and alternated rides and shows constantly. We used the fastpasses as much as we could, and rode things like Small World probably 6 times. My 18mo loved it. The other big winner was the parade and fireworks at night.
You can ask them for a stroller=wheelchair pass and they will tag it as such. You can also ask for shaded waiting, which gets you past the line that is in the hot sun on rides where there is no fastpass. We had both, and many times we ran into staff saying "put your stroller over there for parking." You wave the tag and they beg forgiveness and let you right into the cool air.
We went to the movie studio, but that was really too old for all but my 7yo. Epcot, same thing. There was some neat stuff, but generally, the 2 and 4yo didn't care. We didn't go to the animal park because of the heat, so I can't say anything about that. We did 3 days at Magic Kingdom and still didn't see it all.
Ichthyosis-en-Confetti Type 2
Husband, Nathan - 10, Elliot - 7, Oliver - 4, all affected.
I also have an unaffected daughter, age 8.
email: jennifer at confettiskin dot com
facebook - find me on "ichthyosis mommy spot" or "friends of ichthyosis"