The snorkeling at Chakkanaab (sp?) National Park is great and the restaurant and facilities are great - especially for a family group. We will be there Thanksgiving week with a group of 14 ranging in age from 2 - 68.
Chankanaab is a good family beach, just get there early.
Costa Maya is kind of a work in progress, and I haven't been there yet. With that caveat, I would suggest taking a ship's tour to Xcaret with the family. It's sort of like DisneyWorld with a Spanish accent. Very clean, very well-organized.
Take a look at that option.
pamda -- CM First-Time Cruisers Editor who LOVES Mexico
DO NOT attempt to even hope to find a taxi in Costa Maya. It is a new town being carved out of the scrub. Until recently, workers were transported down to the town daily, the gov. just finished basic housing for locals. Transportation relied on whomever drove down to Costa maya from Coumel that morning. There i a new road, a small airport, limited shops at the pier, a really nice day at the beach or a Mayan ruins tour...havnot heard anything about the tour.