Kittens should stay with their mom until at least 10-12 weeks old. Mom can be spayed at 8 weeks after delivery. Ideally, you should have kittens spayed, neutered, vaccinated, and dewormed before they go to their new homes.
I've heard of Moms who cry looking for their babies. I've heard of Moms who don't seem to treat them differently from other cats in the household once weaned. I've heard of a Mom who attacked her kittens when reunited a few days after her spay. I've heard of Moms who cuddled and cleaned a kitten who was missing for several days like a human Mom would with a missing child.