Don't let this cute face fool you

[Siwsan]

Cute, well, sure. BUT...........


also kind of vicious

[North Shore Chicago]

1. I peek at your kitty posts.

Now is the time to say that these kittens could not have found a better place to be. Thank you for keeping them safe and healthy, you are doing more than your share.

[Phoenix61]

2. That's how they learn not to bite or scratch.

“Social development has a hand in why kittens shouldn't be taken away from their mothers and litters at too young of an age. One of the most characteristic pastimes of kittens is rough play, essentially a type of aggressive play that involves a lot of pouncing, scratching, leaping, chasing and even biting. When kittens play tough, they learn "on the job" about how to use restraint during playtime. This helps kittens learn how not to bite or scratch painfully, for example. “
They suggest 12 weeks.

https://pets.thenest.com/can-kittens-leave-mother-8-weeks-old-9301.html
I had a beautiful cat that I found when she was much younger than 12 weeks and she never really learned not to bite or scratch.