We're having our wedding at Moon Palace next June and like you I needed a resort that was kid friendly. Moon Palace is away from the strip and that was a pro for us. The wedding sales coordinator told me that of all the Palace resorts in Cancun, Moon was the most family oriented and was away from the scene on the strip. When it comes down to it, I think it's about preference. There is a beach that you can swim at but because of its location seaweed tends to creep up. From what I'm told, it's cleaned daily and that many tend to stay by the pools anyways.
I hope that helps! Good luck to you =)