Some enjoy people more than others. The older a ferret is, the more mellow it is likely to become. Young kits tend to be nippy, but no more than a new kitten or puppy. They just nip with more enthusiasm. Some kits never nip at all, but most that do eventually outgrow it.
Ferrets have tough skin and kits have sharp little teeth.
The roughhousing a kit may do with its litter-mates may not be appropriate for its owner's finger. Many new ferret owners mistake this nippiness for viciousness, even though the same behavior in a new kitten or puppy is accepted. There are a number of documented cases of ferret attacks on infants and very small children. Some of these involved serious injury to the child. Parents must either forbid encounters between pet ferrets and their infants or very young children, or closely supervise all of these encounters.