I learned that the hard way when I first got ducks at like age 10. Make sure the fence it tight enough a baby can't slip through, and the male can't get his head through to reach the babies. They will also drown them if given a chance. Then this year I had one duck and two geese sitting. One female goose kept stealing eggs from the other nests. When two gosling hatched in the other nest she killed them both. I had no idea she'd do that, she seemed to want all the eggs so bad. Then a rotten egg broke and killed the rest of the eggs. That goose is in limbo, I'm considering eating her as I'll never trust her. So any males, and any females that are acting "crazy" or stealing eggs, etc, get separated. The males will kill them even at a few weeks old, at least mine have always tried to. I let them get pretty much full size before putting them all together.