If you have a hefty budget, the Dorado Beach Ritz Carlton Reserve is great. The facilities and the beach are the best in Puerto Rico but you will pay sky-high prices.
My father-in-law has been a member of the beach club there for about 40 years, so we are allowed to use the facilities.
They have several great pools, a beautiful beach that is wonderful for small children (I have a 3yo), an incredible pool/ play area for little ones on the Dorado Beach East side, a pool with fountains, water slides and things to climb on, and the spa is excellent. I don't know about activities for the kids because we just spend time with my in-laws when we are there.
A cheaper option would be to rent a place on vrbo.com. Search for places in Dorado, Puerto Rico that say they are located in Dorado Beach East and make sure the house has a golf cart included in the price. I think when you rent a house in dorado beach east, you can get a weeklong membership to use all the hotel's facilities, so while it's not a bargain, it's still cheaper than staying in the hotel.