From the minute you land, there are people to help you set your itinerary. Anything from swimming with the dolphins, a bus ride through the Yucatan Peninsula, deep sea fishing and there is always snorkeling and diving that are unforgivable. There are more relaxing things like renting a scooter or a car and taking a lap around the island.
A ride through the Yucatan Peninsula is a good way to start the first adventure. Catch a fairy over to Playa Del Carmen and hop aboard a bus or a tour van, to start the day long adventure through the peninsula. The mode of transportation is up to you and your preference or budget. Taking a tour bus can be less expensive or maybe it would be more enjoyable for your group to hire a tour van. With a tour van they will give you some options on points of interests so the tour is designed for the group's pleasure. The trip could range from organizing a tour to Coba and Tulum and a stop for snorkeling at Akumel. Chichen Itza is a Mayan ruin that is definitely worth seeing and a learning experience as well. The Yucatan Peninsula has bird sanctuaries, eco parks, caves and much more. Just a ride through the peninsula is worth the experience, to see the culture and how the people in the area live.
If it's all about the underwater activities then Cozumel is the right place to go. If you did nothing but a snorkel trip to the reefs it would be time well spent. Just snorkeling off the docks at the hotels is a real treat. The marine life off the docks is abundant with water clarity up to 200 ft the view is incredible. Scuba divers will love this island too as it offers scuba dives that make life long memories. Bring your diving camera and a lot of film because the photo opportunities are incredible.
Renting a vehicle and cruising to the other side of the island is always fun. The other side of the island could not be more different and just the drive itself can be entertaining. The opposite side of the island is a good place to sit and watch the waves roll in and relax. You will need to take some sun block because the sun always shines at Cozumel.
Take what you can with you because the prices go up on the island. Buy your snorkel gear before you go especially a dive mask and snorkel. It is not fun to rent a mask that is worn out and a snorkel that has been in someone else mouth. Renting fins is usually alright but it can be a bad experience too. Snorkel gear does not take up much space in your suitcase. If Dr Pepper is your favorite soda you might want to take it with you because it has been my experience that it is hard to find and expensive when you find it. That is the case in Mexico in general. Buy your scuba gear, dive equipment and book your trip now because spring is a great time to go to Cozumel. Take the family on an experience not just a vacation.