We spent this last weekend in a hotel in North Dakota. I have a 3 year old and a 4 year old. They swam in the pool for a couple of hours and everyone collapsed into bed at 7:30 - including me.
At 12:30 our next door neighbors came home from whereever they were. A family with teenagers. Boy were they loud! Although I don't think they were purposely loud, they were talking in normal teenager voices and moving around getting ready for bed and laughing about their day. But, at 12:30 in the morning, it was loud. They didn't wake the kids, but woke me up.
We, of course, were wide awake by 6:00 - the kids were really excited to get into the pool and couldn't sleep any longer! (imagine being at Disney or what its like Christmas morning!) We were as quiet as possible with two hyped preschoolers, the pool didn't open until 7:00 and there wasn't anything to do except stay in the room and try to keep the kids distracted. Though the three year old did have to have a tantrum about something or another - and the four year old did manage one leap from the bed before getting scolded. Plus my mom plugged in her blowdryer at 6:30 to get ready - if I could hear their TV at midnight, they could hear our blowdryer at 6:30. I'm sure we woke our next door neighbors and has them complaining about their inconsiderate neighbors who get up too early and can't keep their preschoolers under control.
I'm not sure you can do anything about it. It is not reasonable to expect them to adjust their children's routines because sleep in - any more than if you occupy the upper floor, you are going to arrive home before their kids get in bed so as not to wake them coming back from a late night at DisneyQuest. If you spoke to them, they may agree to try and keep their children quieter in the morning, but you need to be prepared to realize that even well behaved preschoolers of responsible parents are going to be hyped and running around getting ready by 7:00am at Disney - and there is only so much they can do.