I came to Las Vegas with three girlfriends in July 2013 and we probably spent at least five hours at the Monte Carlo pools over the course of three days. We rented two inner tubes to share, and spent the majority of the time circling the the lazy river. There were a few kids around but it actually seemed to be more adults just looking to lounge. There are plenty of beach chairs around if you get to the pool early enough (by noon).
We stayed out of the wave pool since it seemed overly crowded and kind of boring since you couldn't bring floaty toys in. There is also a sand volleyball court but it was too hot (100+ degrees) to even think about playing in the sand. There was a DJ on one end of the pool but it wasn't too loud if you weren't right next to the speakers.
Our primary disappointment was the poolside food and beverage service. We wanted to order nachos and sliders but we couldn't find a waitress!! We tried repeatedly to flag one down but they ignored us. My friend finally chased one down but she said she wasn't working our section. She said she would send the designated section waitress but no one ever came. I realize we weren't in a cabana but I didn't expect to be completely ignored!! The food and drinks are overpriced and mediocre. One plus: They have free ice water over by the bathrooms - that was a nice touch.
I had researched getting a cabana (and was actually serious about it) but the price was just too much and it turned out I was glad I didn't. We had an easy enough time getting four chaise lounge chairs together and were able to enjoy the pool for free and spend the money on other fun stuff ! ;)