You might try the Crown Paradise Club. The one in Puerto Vallarta is better for younger kids. With kids the ages of yours, the one in Cancun is better. They have a water park for the little ones and a water park (it has two slides) for the older kids. They have a volleyball court (sand) and other fun activities, of course a few pools that aren't too big, but we were happy with them. Having said all of that, the CPC Cancun is not that nice. It's probably on par with a Holiday Inn. There are some issues with rust thruout the hotel and it's not in perfect shape. The price is not bad and I think you can get a suite for a family. I'm not sure as we were just 3. This year we are trying the Gran Caribe Real in Cancun. We haven't stayed here before, but the reviews on trip advisor. com are better consistently and it looks nicer. We got a great price, but they may have been having a promotion. Again, they have a couple of water parks for kids of varying ages. Check it out (look at the photos link to the right of the page next to where it says Rating and Details): http://www.tripadvisor.com/ShowUserR...ECK_RATES_CONT
I hope this helps. Feel free to email me with questions is you want to. Have a great trip! Be sure to check out Funjet Vacations, We are actually taking Mexicana Vacations as Funjet was using their flights anyway. Was slightly less expensive, but not much. Continental has a vacation company as well as other major airlines.