Cancun is hugely popular destination, and many families stay at all inclusive or other resorts in its famous Hotel Zone or nearby. Wherever you stay in Cancun, be sure to get out and do some of the interesting day-trips in the area!
It's easy, for instance, to take a local ferry to laid-back Isla Mujeres: so close and yet a world away. Rent a golf cart, explore the island, have lunch at a beach restaurant....
Or head south to the Mayan Riviera, to see Mayan ruins at Tulum, or explore the Si'an Kaan Biosphere Reserve
, or have fun at one of the eco-parks such as Xel-Ha or Xplor. The Xcaret eco-archeological theme park is a big draw: plan to spend the whole day, swim the underground river, and stay for the excellent night-time show.
See these and more ideas at Cancun: Things to do on Family Vacations