MMM:I love Las Anclas. Didn't realize they had a no kids rule (thought I had actually seen some but not many) but it's probably one of the reasons I like it so much. But it's really not oriented to kids anyways - unless you want to spend 24/7 entertaining the rugrats. There's no pool, no recreation director, no loud music etc. etc. etc.
I don't know that it's a hard and fast rule, but that's what he told us when we visited with him last month. Either way, it's a really nice place that I wouldn't have a moment's hesitation in recommending.