Kittens have particularly sharp claws since they're so small, and until they've been trained using the "screaming in pain" method, they see no reason to ever retract them. Our kittens were pretty affectionate, which you think is a positive until you realize more affection means more scars. It's been almost two years since the kittens left. Here's my leg today:
There are two types of scars they'll give you. The first type of scar is a puncture scar, from kittens climbing on your lap and just not bothering to retract their claws. You get anything from minor pincushion pokes to deep blood-drawing punctures. It takes most cats a while to learn the difference between sitting on a person and sitting on an inanimate object and appropriate claw positions for each case. Although you have the occasional cat prodigy, like Kirk, because Kirk was the best cat ever. Keep this in mind for later.
Capt. James T. Kirk: Best Cat Ever.