I see you are from IN. Summers are warm for you but here in late August early it's like 2 degrees cooler than walking on the sun.

We don't have "indian summer" we have Hot, HOT and HOT. with humidity to boot. I don't want to alarm you but you need to be prepared. The sun is very hot so prepare by bringing extra sun screen. Most people do not apply enough through the day and get burned. The hottest time of the day is mid day but we normally get afternoon thunderstorms EVERYDAY between 3-5-ish. They typically only last about 30 min or so but you may want to invest in some ponchos ahead of getting to the parks. They charge an arm and a leg for them inside.
If you can take mid day pool/nap breaks, I recommend it. Early and late are the best plans of attack. Bring mosquito repellant. You'll need it at night.
And lastly, I can not stress this enough. Drink water. Like 2 times the amount you are use to. Water at the counter service places all over WDW will give it to you free so use it to your advantage. It is not tap water but it comes from the fountain that the soda is served from.
You can not hydrate enough and if you wait until you are thirsty, it's too late.