We took Dnience and DNephew when they were 8 and 6, and again when they were 10 and 8. I have to say, the trip when they were 8 and 6 was more fun, because they were still just a bit younger and into all the Disney things - a couple years latter, they were a bit more into being "cool". I think it is easier when it's not your own kids - DNephew learned from us pretty quick that whinning would not be tolerated. DH got as far as the park enterance with him on the second day - taking action after threats to return him to the room and park him with a babysitter for the day. DNephew decided at that point to apologize, and he did very well with whining for the rest of the trip. We did not have to worry about them being afraid of rides (except the more roller coaster type, plus Dinosaur in AK), but they were good sports about it. DNephew did manage to walk the whole time, but he is into sports, so I think that helped. Overall, I think the trip was such an amazing experience for them, that it put them on their best behavior.
Plus, helps that I planned either an early dinner or lunch break at TS every day, to give us all a well needed 1 hr + to sit in AC and relax. Also, we went in April, which was very nice weather wise. Next trip was late Sept. and much harder for the kids with the heat.