There have been many posts on this subject. The aft pool on the Fantasy is designated as "adults only" and it is even listed that way in the Carnival Capers. That is where the adults only part ends. Parents bring all of their rugrats to that pool and glare at anyone who dares to voice any opposition. (you are supposed to find their offspring as cute and adorable as they do) By the second day of the cruise, the "adult" pool is completely filled with kids dropped off by parents who don't want to walk all the way to the main deck pools. If you want an adults only pool experience on the Fantasy, I suggest you get a room with a tub, a bucket of beer, and play reggae music on a cd player.
P.S. Don't tell anyone of the bathtub "pool" in your room or some parent will be banging on your stateroom door wanting to drop their kids off with you so they can head to the bars or casino.