Just returned from a 7-day western on the Magic. There were tons of kids but they were usually very in control). I hung out at the adult pool on sea days and my husband and I did the adults only clubs at night so the kids were really not a problem. Both my teens had a blast in Common Grounds and their activities.
One note - children under 10 or 11 should NOT go on the Tulum ruins excursion in Cozumel. It is long, warm, and fairly rough walking. Some younger ones just did not appreciate the historic and cultural significance, they really wanted to be swimming. One baby just cried and cried. I plan to let Disney know that this warning should be on the excursion literature.