Cozumel works well with children for a reason that has nothing to do with kids' clubs: the west coast is a sheltered, shallow, bath-warm lee with reef inside swimming distance of a sun lounger. A seven-year-old in a snorkel vest can float over parrotfish, sergeant majors and brain coral at Chankanaab or Money Bar at Dzul-Ha without ever getting on a boat, in water that sits between 78 and 86 degrees all year. That is an unusual thing to be able to say about a Caribbean island, and it is the core of the case for bringing children here.
Two constraints shape every family plan on this island, and both are safety rather than preference. The east coast is not swimming water. It faces the open Caribbean, it has serious undertow, there are no lifeguards, and the few pocket bays that are calm on a still day are not calm on a windy one. Go east for the drive, the beach bars and the limestone arch at El Mirador, and keep children out of the surf. And the reefs everybody talks about are drift sites. The current that makes Cozumel's diving world-class is the same current that makes an unsupervised child in open water a bad idea. Family snorkelling belongs at the sheltered sites — Paradise Reef, Chankanaab, Dzul-Ha, Playa Corona, the El Cielo sandbar — with vests on and an adult within arm's reach.
Age gates matter here more than at most destinations, because so much of the island's inventory is diving. Bubble-blowing pool programmes generally start around eight, introductory resort dives and junior certification around ten, and most dolphin encounter programmes set both an age and a height minimum. Snorkelling with a flotation vest works from about five or six for a confident swimmer. If your child is younger than that, the plan is a beach club with inflatables and a shallow entry, not a boat.
The reliable engine of a Cozumel family day is the all-inclusive beach club, which is the island's best-selling product for good reason. Mr Sanchos, Playa Mia and Paradise Beach all combine calm leeward water, pools, food that solves picky eaters, shade, real restrooms and inflatable structures children will not leave for four hours. Expect around $79 to $85 per adult at the large clubs with teens and children stepped down substantially. Expect music and a crowd on a four-ship day. Do not expect a quiet stretch of sand; that is not what these places are.
Two smaller things worth building in. The sun here is equatorial and reflects off the water, so rash guards do more work than sunscreen. And Cozumel's afternoons in the wet season deliver a short, heavy downpour most days, which is a good reason to put the water time before lunch and the shade time after it.