in the same boat. With three school age boys, we have to usually go during the July/August timeframe also. Plus, our two oldest have birthdays in late July and late August, so we tend to go in between. The first time we went the two oldest were young and we didn't have the third one yet. We stayed in a Wilderness Cabin on property. As many on here have stated, we would get up early and have cereal, frozen waffles, juice, etc before going in the parks (cabins have full kitchen). We would do the park until it started getting really crowded/hot (different times each day) and then go back out to the room, grab a sandwich, and take the boys to the pool to cool off. We would then go back in later in the day when the crowds and heat were dwindling, and we could enjoy the late evening parades and fireworks, grabbing something to eat in the parks.
This past year we were there the end of July/ first part of August. With the two oldest being old enough to fend for themselves somewhat, they would take off and do things at their pace while we took the 10 yo around with us at a slower pace. They had a cell phone, and we always had certain times to get back together or check in with each other. There were a couple of days that were very hot, but most of the rest weren't too bad (relatively speaking). It is very doable with a little bit of planning. There are a number of websites, including this one, that give tips about which days to do which parks (we stayed with this stringently), and other tips about maximizing your bang in the allotted time. We would head out to the more popular rides first and at least get a fast pass if the line was already pretty long. This helps tremendously to turn a longer wait for one ride into a benefit that you have basically already put in your wait time on another ride. With proper planning(check wait times and fast pass times to decide the best option) the wait, crowds, and heat are all very manageable, even during this peak tiime of the year. Water bottles, ponchos, small battery fans that hang around your neck and those spray bottle fans are all great ideas you don't want to ignore.