RomanC,
You already know cozumel and should try now Playa del Carmen. June is getting to the end of the wind season you are right but we actually have a very good end of season so far with a lot of steady wind and perfect weather.
A perfect family spot would be to stay at the Sandos Playacar Resort, in Playa del carmen itself!
PDC Kiteboarding School is located right on the beach in front of the resort!
http://pdckiteboarding.blogspot.com/ From there you have about a mile long of private uncrowded white sandy beach to ride. The resort offers everything you need for kids and no-riders!
In case of no wind, you can Scuba dive, snorkeling, sailing, wave running, parasailing......etc.
5 min away from there is the world famous "Quinta avenida", the busiest pedestrian avenue in Mexico where you ll find restaurants, shops, beach club, and a lot of night life!

