Yes, it's doable. Yes, its hot, yes it will rain, yes you are going to have melt downs at some point but it's doable.
I was there from 8/28 thru 9/3 last year and everything was a walk on, I mean the longest wait I had the entire week was EE for SDMT which was a hour and I got there maybe 10 min. into EE and 20 min. for Little Mermaid. Otherwise, everything else, including Rise and PP was a walk on. To be fair, I had hoppers so there was an advantage of being able to repeat parks at night. I always take breaks in the afternoon, we always have. Summer hours the parks are open later so that is to your advantage. If school hasn't started yet there will be crowds.
Just be prepared with some way to try to combat the heat, lots of water (free in the parks) maybe
cooling towels or small fans (especially for the little one). Ride things with AC as often as you can. Be prepared to wait in lines, we don't have problems with lines since we have been going since long before any kind of FP system so if you wanted to ride a ride, you waited in line. Will you do everything in the parks? No, but lets face it, even if you bought
Genie+ and ILL you probably wouldn't do everything there is to do. It's possible to ride every ride with Genie+ and ILL if you go from park opening to park close and not take a break and cross all over the parks but that is exhausting. And that is still not doing everything in the parks. Maybe pick two or three rides in each park that are must dos and go from there.