I've had the same experience on Carnival — no enforcement of the adults only pool. I hope no parents take offense to this, but it frustrates me that that rule is not enforced. I like kids, but as a married 20-something with no children of my own yet, I sometimes want to relax in a child-free environment. There are more than enough other pools to occupy the kids.
On the Conquest, kids were often running around the pool area, completely unsupervised, doing cannonballs and splashing all of the sunbathing adults at what was supposed to be the adults only pool. I asked at the desk who was enforcing the rule, and the woman blinked up at me and said, "The parents?" Yeah right...they were nowhere to be seen.
On Caribbean Princess, there were never any kids in the adults only pool, but I think it was more because the pool was aft and shadowed by a nightclub a few decks up, which made it perpetually cold. Fine by me, though!
Booked on Carnival Freedom, Feb. 2012 (Cozumel, Costa Rica, Panama)
NCL Gem, Sept. 2011
NCL Jewel, Feb. 2011
NCL Dawn, Sept. 2010
NCL Spirit, Feb. 2010
NCL Gem, March 2009
RCCL Explorer of the Seas, Feb. 2008
Carnival Miracle, May 2007
Carnival Conquest, April 2006
Caribbean Princess, Feb. 2005