My three kids are “sinkers.” They’re all adopted and all Asian. They also have no fat.
I never could teach any of them to float the way my mom taught me. We gave them swim lessons, but it was a struggle for the first two to learn the lessons in the order presented.
But they all swim now. My youngest somehow figured out how to swim underwater and that was the key for the older two learn. Maybe sinkers need to learn to swim underwater before they get up some enough speed to learn to swim on the surface.
I never could teach any of them to float the way my mom taught me.
Video here.