We only took one little one, but she was 25 months, so hopefully I can offer a few tips.
1. Be prepared to go back to the resort for nap/rest/pool time. This isn't something we did every day, but we kept it open as an option each day depending on how DD was feeling. The days we went back we were frequently able to stay at the parks later and most of the little kid rides seemed less crowded late at night (we"ve walked on dumbo right before closing on several occasions).
2. Speaking of lines/crowds - we did our best to avoid them. We traveled during off season, picked days with lower expected crowds, and got to the parks at opening/shortly after (rope drop was always the target, but sometimes we'd be 15-30 minutes after). We did the rides that we knew would build up a line early in the day so eat could do stuff without lines later on.
3. Bring lots of snacks, sippy cups, etc. You never know when your child will go from fine to famished in no time flat, so come prepared. Those applesauce/fruit pouches are amazing, so are raisins, crackers, Granola bars, etc. we made sure DD's sippy was always full of water (and could also use it for milk at restaurants).
4. Bringing food for breakfast in the room (oatmeal is super easy, we also go juice, donuts, etc.) makes for easy mornings, which you want if you are trying to get there early (then we were hungry for earlier lunches and could avoid the rush).
5. We like staying on-site, that makes it a car-seat-free vacation for us, the busses are weirdly efficient in the parks and I LOVED that you could check your bags through to your resort with DME (seriously...amazing when traveling with little ones and all their stuff).
6. Bring at least one stroller. We brought a maclaren (our normal to-to stroller) and loved having it. We could store our toddler stuff (snacks, diapers, change of clothes, etc.) in the basked underneath and not have to worry about carrying it. We also parked the stroller a few times and would wander around a bit without it then come back and get it (obviously don't leave valuables in it or anything

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7. Look at maps and figure out the parks/what attractions your little ones might like. DD is into Doc McStuffins, so once we did our top DHS attractions (rock'n'roller coaster, TOT and TSM) we went to the Disney Junior show to make sure we didn't miss it. She loved it
