Okay, I'm just repeating what I've been told. That the reason you see ducklings swimming with their moms is that they get waterproofed by the oils in her feathers getting on their down when she sets with them under her wings. But brooder ducklings don't get that, so they shouldn't be allowed to go in deep water until they get their own feathers. I know that chickens have oil glands & preen some of it into their feathers, & wondered if that would be sufficient to give their ducklings some bouyancy. But maybe I don't have the facts right.
I know I love to watch my ducklings play in shallow pans of water, and afterwards preen themselves all over. I wonder if they do that cute little stretch & tail waggle to stimulate their oil glands there. It seemed that the fluff above the tails of my brown Khaki ducklings would darken in the spot above their oil glands after they did the wiggle, and then they'd rub their bills right over that dark spot, then over their bodies.