A litter of kittens is typically referred to as a kindle. A kindle is a group of kittens born to the same mother at the same time.
A kindle typically consists of between two and five kittens, although larger litters of up to 10 kittens are not unheard of. Kittens in a kindle are usually born within a few days of each other and are all related. Kittens in a kindle often look and act similarly, as they will have been raised together by their mother.