We went last year with Luke, 8. We only did Epcot, so I only have suggestions for that place.
He absolutely positively LOVED the Agent P thing. They get cell phones that gives them a clue as to where the next clue is- anywhere in the park. Then, at the end you solve the case just like Agent P. Luke did two of them, he loved it so much. The coolest part about it for me was when you got to the location of the next clue, your cell phone made it to something- ie the skeleton would dance when you told it to, a secret code or message would light up in a painting, etc. It was a LOT of fun.
We ate at both the Mexican place (window service) for lunch and the Italian pizza place for dinner. THe pizza was a-maz-ing. As was the Mexican food, but the pizza. YUM.
Luke wanted to add that his favorite town was Mexico. He liked the boat ride and the little market inside the pyramid. Hee hee.