I am on ASD, I have been going since I was very little. One we all react differently. You may find that your DD's can do a lot more than you think, I could at a young age, at home I was always in meltdown but take me to Disney back in the days with no
DAS and I was fine for hours. For my the constant change kept me wanting more, although I know some on the spectrum are opposite. I would not put a time frame on how long your dd can last until you get there.
Second, as other suggest, get there early, rope drop, since your children are 3 and under, you won't really be waiting in the lines that get two hours or longer. And early in the morning you will be able to get on just about everything dgd will want. I remember in DL when my mom would take us at rope drop and we road everything in fantasyland before the park opened to everyone, with MM, or whatever it was called back then. She then got a few fast passes and did things in between, like a charactor breakfast at 10, and a ride on the boats at 12. By one we had done almost everything I could go on at 3 and we headed back for a nap and a swim and dinner at a resort. Then back to the parks for the fun night rides and fireworks, we always did jungle cruise and haunted mansion at night.
I never went to WDW when I was little and it is much bigger, but I am sure you could get on almost as much in the am there also. Just space it.
Also, have things she can use while in the stroller or walking, my mom always made me walk because I had so much energy. But she gave me oh know my brain went died, those bendy flexible sticks, pipe cleaners or something and I would play with them, or one of those things that have numbers in a square and you had to get them in order from one to nine. It always took me 20 minutes or so and by them we were at the top of the line.
Also brings food and water in, times goes faster when you are eating so 20 minutes when eating gold fish seems like two. Also, if hot in August bring a change of cloths, there are still those water park places, correct. Sorry my ASD has a hard time distinguishing between WDW and DL, so I am trying to keep it general, but there use to be the water ball, or the tug boats with water play, or the sprinkles coming out of the ground, that breaks up the mood, cools her off and helps her refocus when you get back in line.
Hope this helps. Not to many grown ups who can tell you what it is like as a child with ADS, and I know we are all different, but here is my thoughts and things I remember from DL as I was small, I didn't go to WDW till I was 14 or so, and little kids rides where not my thing then.
Oh I'm new here, but a huge Disney fan and know quiet a bit. So you know I have ASD but my boyfriend uses and
ecv, when there because he was hit by a Mac truck when he was young and still has joint problems, and head injury problems.