Ducks imprint on the first largest (usually living or moving) thing they see when they hatch. It's usually the momma duck and their siblings. they understand then that they are a duck. If they see humans, they'll think they are humans, but the instinct of being a duck is so strong, they will...
we always separated our ducklings in different brooders. That way they bond better to a specific human. One Human per Duck seems to work best (though one human can have several bonded ducks to them. I have three )
After the first week or two, they will begin to bond to each other rather...