I don't know for sure that this is true for ducks, but this is the time of year when wild birds are "fledging" which means more than just learning to fly. The parents are starting to teach them independence, and for many species that means they may be entirely alone for a day at a time. For that reason, it's incredibly important to be very very careful about removing baby birds from the wild--the parents are probably coming back for them.
I would leave the ducklings on the pond (putting out some chick feed won't hurt though, and may encourage them to stick around and make friends eventually). Watch them until nightfall (where are you that it's not nightfall yet??). If the parents do not come back, then you will need to see if you can get them somewhere safe for the night.
How old are the babies? Do they have feathers? Pictures would be very helpful in providing more detailed assistance.
Good luck!