We have been to Cancun/Riviera area many times and my kids favorite was the family suites (adjoining rooms) at the Beach Palace. Their next favorite that we took a trip to in Feb. for the 2nd time is the Gran Caribe Real, they love the kids activities, the fact that its a smaller resort, the beach and water park. We have also been to the Great Parnassus which is very kid friendly and budget friendly, but it was loud (shaped like a cruise ship) but busy with familys. We have also been to Crown Paradise...........
My kids have loved every trip and we always enjoy them as well. We like certain things at certain resorts and depending on the budget (we go for 10-14 days each time) we have been happy with all our choices for what the trip cost.
Many resorts also have kids stay free in the summer.............