Like others have already stated, I have ALWAYS handled the kittens from day one. Maybe not a lot, and definitely watch mom's body language. Maybe do it in a quiet, closed room, don't make sudden movements, etc.

Also remember if mom gets too stressed she may move the kittens, so keep them somewhere where there is not a lot of traffic, and closed off to other animals.

Make sure to wash your hands before handling them though so they don't get sick