best beach for 1 day in Cozumel

Hi all, Im heading on a cruise with my dad (70) and my son (9) and we'll have 1 day in Cozumel. My son would love to get to swim with dolfins or pet manatees or whatever like that, but my dad just wants to sit on the beach and chill. Is there a beach where I can go, leave my dad on the beach and do these kinds of activities with my kid? thanks!