Got back a few weeks ago from a trip with my 5 year old son (and 2 year old daughter, but that's not as helpful to you

)
His favorites:
MK:
Buzz Lightyear Space Ranger Spin
Haunted Mansion (he still will tell me about the ghost that followed us home)
Pirates of the Carribean
Tom Sawyer's Island
Small World (really!)
He liked 7DMT and Thunder Mountain, but much preferred Buzz over the roller coasters
For the 4 year old, Tomorrowland Speedway. They were my son's favorite at 3.5. This time he enjoyed them but wasn't nearly as excited. (BTDT syndrome, I think)
Epcot:
Agent P Missions. I can not stress this enough. Leave some time for your kids to do at least one of them. They are the perfect age.
Spaceship Earth (really!)
Soarin
The Nemo Ride
Surprisingly my son didn't like Turtle Talk with Crush at all, but he's really shy sometimes and didn't want to sit with the kids on the floor. I think most kids that age love it.
Animal Kingdom:
The Explorer Scout Badge book. He absolutely loved doing it and getting the badges. It also is a great way to really explore the park in a little more depth.
Walking the trail and looking at the birds and animals after the Safari. (He liked the Safari too, but really loved the trail)
Dinosaur. This will vary A LOT by kid, so determine for yourself if your kids will be too scared for it.
The dino dig play area. The 7 year old may be a little old for it, but the 4 year old will love it.
Hollywood Studios:
Toy Story Mania, of course
Star Tours. Star Tours. Star Tours. Star Tours. He rode it four times. And wanted to go again. Hands down his favorite ride in any park.
Hope this helps!