Our 1st trip with the kids was in 05 (just started planning our next for fall of 08!). DD was 3 and DS was 4 - every kid is different and you really must know your child - but musts for my DD were:
Dumbo & Alladdins Carpet Ride (basically same thing!)
Race Track in MK (she drove!)
Carousel
Princess Breakfast in the castle - she dressed up as Cinderella and LOVED THAT!
Country Bear Jamoboree
Tea Cups
Poohs Playground
Playhouse Disney Show
Playground in MGM
Safari in AK
Kids area of the water parks
I had also picked up a cheap
Walmart crown/tiara she enjoyed wearing all over the place - even with shorts & a T-Shirt!
She did not like anything she could not see what was going to happen in - even Snow White, Peter Pan, etc. If she couldn't see what the ride did out in the open she wanted nothing to do with it. 3-D Movie shows - Tree of life, Mickeys Philharmagic I think there was screaming involved

She also LOVED doing the character meet and greats - autographs galore, and pin trading. Best advice is take things at the childs pace. As the adult we think they will like certain things but you really need to take a Q from the child. It took us a day to adjust to how she saw WDW but it was a time we will never forget!
