I took my then 12yo DNiece several years ago after she finished 6th grade. She was very homesick. However, it was her first time away from her parents, first big trip, first plane ride, too many "firsts" I think. On the flipside I am taking another DNiece next summer who will be 6yoand don't anticipate any problems. She and I are together almost every day and it is almost like she is mine. I've taken her to WDW 2x already although with other adults and also took her 1000miles away to visit relatives this past summer for 2 weeks. She has never been homesick or even asked for her parents, not even the first time we took her to WDW when she was 2. The point I'm trying to make is that I think it depends on the personality of the child and how much time they've spent alone with you and have been away from their parents.
By the way the time I took the 12yo we stayed at CBR and were fine. I also stayed there when I took the 2yo. I like the resort. Not sure where we're staying in 2012 yet.