You are going at one of the busiest times of the year. If you don't mind waiting in line for 30-90 minutes for one ride, sleep late. If you want to try to do as much as possible before the crowds get awful, go as early as you can. Fast passes run out as the day gets on. Lines get longer and it gets harder to find a place to eat.
Convince your son that going to bed early or taking a nap is the wisest move he will ever make.
We never wait in lines more than 15 or 20 minutes. It's just not worth it. You get tired, the crowds get crabby and it's not any fun.
My 10 yr old son sleeps until 10 or 11 on Saturdays if I don't get him up. But at Disney, he's up when his dad and I get up. We hop the bus, hit the parks and do what we want to do. About 11 or 12, we head back to our hotel, make some lunch and take a swim or watch some TV. Maybe take a nap.