Kathryn,
For your answer, let me start with a personal experience;
When I took my girls the first time as a 'whole' family, they were just a month shy of 3 and 5. I was insistent that we get a room with a balcony. The thought was that we needed to have somewhere for my wife and I to go after the girls had gone to bed. I even got a little battery-operated lantern so we had light to read and play cards by.
Never went out there one time.
The day was exhausting enough for all of us that everyone went to bed at the same time. There was no need for a separate space for us to go after bedtime. Any my girls never kept each other awake with all the excitement, simply because they were that tired. So a standard room for us was just fine.
But you may have an early enough bed time for your 12 month old that leads you to wanting to have him down before the other 2 kids? I totally get that. So the quickest idea is to get a Family Suite at the
Art of Animation. You could put the baby down in a pack n play in the master bedroom so everyone else can stay up in the living room space. You could also look at some 1-bedroom accommodations in the Deluxe Villa resorts. The best for you with young kids would be in the
Bay Lake Tower at the Contemporary, so that you were close to the Magic Kingdom. But many other options are available.
Write me back if you have any follow-up questions!
Have a magical vacation!