The two mother ducks are teaching the  three ducklings how to swim.  Contrary to popular mythology, ducklings are not “waterproof” when thy are born and can easily drown as their baby feathers are fluffy and do not have an oily coating.  So we are careful that water is available for drinking but not deep enough for drowning.  Now that the ducklings are beginnng to grown their adult feathers they can test  the water and learn adult duck skills.  Very cute.