Kitten

The sex of kittens is usually easy to determine at birth. By six to eight weeks they are harder to sex because of the growth of fur in the genital region. The male's urethral opening is round, whereas the female's is a slit. Another marked difference is the distance between anus and urethral opening, which is greater in males than in females.
Kittens are highly social animals and spend most of their waking hours interacting with available animals and playing. Play with other kittens peaks in the third or fourth month after birth, with more solitary hunting and stalking play peaking later, at about five months. Kittens are vulnerable to harm because they like to find dark places to hide, sometimes with fatal results if they are not watched carefully.
Although domestic kittens are commonly sent to new homes at six to eight weeks of age, it has been suggested that being with its mother and litter mates from six to twelve weeks is important for a kitten's social and behavioural development. Usually, breeders will not sell a kitten that is younger than twelve weeks, and in many jurisdictions, it is illegal to give away kittens younger than eight weeks old.