A baby duck is called a duckling. A small duck is considered a duckling until it reaches adult age, beginning at approximately two months from the time they hatch, depending on the type of duck.
There are several breeds of ducks and variations in the age in which they are considered adult. For example, Pekin ducks grow rapidly and reach 90 percent of their adult weight at seven weeks of age, according to the Duck Research Laboratory at the Cornell University College of Veterinary Medicine. While a single baby duck is called a duckling, a group of ducks or ducklings may be referred to as a brace, flock, raft, paddling or badling, according to the U.S. Geological Survey.