Being a local, the advice I would give you for July or Aug. would not be the same as Sep. The humidity starts to lower in the fall. Also shorter park hours means taking breaks at the parks. Watch the youngest and when they show signs of wearing out, then find a sit down shady spot and have a Mickey Bar or drink.
We always plan a "Resort Day", no parks. This gives the little people, and you, a chance to catch your breath. We have a late breakfast, hang out at the pool, have a nap and late dinner. The next day everyone is ready to charge out again.
If you have not done so, bookmark the Disney site. You can download park maps, do the PDF version. Then study them so you have a good idea what you want to see and what part of the park it is in. If you walk AK from gate to each section back to the gate you will have walked 9 miles.
So to cut down on wasted steps and time, get to know the park before you arrive. Also check the park hours up to when you head down. They can and do change right up to the 1st day of the month. When you check in ask for Park Hours Sheet, this will give you show times and the like.
Welcome and have the time of your life. This link will help all of you get into the mood from a ex-Peorian
http://www.geocities.com/Broadway/Stage/7840/select.htm