I have three children. All of them first swam under water. First with my help then soon they learned to emerge to breath.
All of them loved little toys to dive from the ground. And with that they automatically learned to come to the surface again to breathe.
And as well they soon learned to dive from the edge and swim to me (or back to the edge) under water.
My youngest daughter had a snorkel. She loved it but anyway she didn't use it much. Toddlers every few minutes have new ideas they want to try, a snorkel was annoying. Snorkel on, snorkel off, snorkel on.... My child hadn't the patience to hold still while fixing the snorkel.