I agree the Occidental Grand Xcaret is nice, but we stayed at Dreams Puerto Adventuras this last Christmas and really liked it.
-It's in a gated community about 15-20 south of Playa Del Carmen. You can walk to the marina and swim with dolphins, see the manatees and sea lions.
-They have family rooms, but we just have one kid so a regular room was more than big enough.
-It's on an inlet, so the beach isn't too rough or deep. They have a water trampoline and climbing iceberg in the ocean for kids to frolic.
-They also have a natural pool with various sea critters. You can feed the fish, they are super tame and friendly.
-Food/drinks were good. 24 hour room service, minibar, and several restaurants to choose from without having to make reservations. Top shelf booze for mommies and daddies and a specialty kid drink of the day
-Great kids club. This was the big deal for us. The kid club was well staffed with CPR/Red Cross certified English speaking staff. There was a diabetic little boy there at the same time we were and they were able to check blood sugar/insulin etc. They have a daily schedule with activities every day. They will take the kids to meals if you want some alone time too. You get a pager when you drop them off, and you have to be buzzed in to enter.
-There is an Adult side of the resort with a quiet pool and bar if you have childless family members traveling with you.
-Entertainment. Every night there was a huge screen on the beach with movies/popcorn. There was also a theater with shows, circus show, Elvis impersonator, etc. They also had an American Idol type contest too.
It is an older/smaller resort, but it has been fully renovated in the last year or so. I liked that the resort is smaller. If you forget your camera, or want to quick change before lunch it's a short jaunt to the room. The Occidental is huge.
If you have a party or 5 or more, and plan to take an excursion, it would most likely be cheaper to rent a driver for the day. We went to Chichen Itza and a cenote. 10 hours private transport, lunch, guide, all on our schedule for less than the cost of a bus tour.
Let me know if you have any questions.
Have a great time!