These sound like awesome recommendations! As far as snorkel gear, check with your charter company - I only have experience on sail boats with BVI Yacht Charters, but they always have mask, fins, snorkels included with the boat - their system is they have a box full on the dock, and everyone just grabs what they need before leaving… you’re right about fins for kids, but I find about a 50/50 preference for or against fins anyway, maybe rent some kid fins to fill the gap…

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There’s nothing, absolutely nothing, half so much worth doing as simply messing about in boats.