Grand palladium Kantenah in the Mayan Riviera. I went before kids and loved it, and friends have gone with kids and loved it. Excellent food, resort, pools, etc.
I've been to The Reef twice, in 2010 and last year. It is a small (only 200 rooms) AI about 5 min from Playa del Carmen. First visit, we went with my nieces and nephew (aged 6-15) and they had a good time.
Last year, they were in the recess of renovating the bathrooms and we got one of the renovated rooms. OMG! I wanted to put the shower in my carry on! I could have lived in there!
There are about 12 buildings or so, all only 3 story. The buildings meander through a garden leading to the pools, beach and restaurants.
First time we went, a week there was about $700 each. Last time, it was closer to $1300. I think it is being 'found'.