It depends where the ducks are:
In flight: flock
On the ground: brace, badling, or sord
On the water: raft, team, or paddling
Chicks: brood or clutch
A female duck is called a duck, or, as a female bird, a hen.
A coot ( a type of duck) when in a group is referred to as a: cover of coots.
A runt duck is simply referred to as a runt, as "runt" is a term used to describe the smallest or weakest animal in a litter or group.
A single baby duck is called a duckling, now make that plural. A group of ducks, however, is called a balding.
A female duck is called a duck or a hen as a male is called a drake