One of the inherent nature of instincts in mammals is maternal, which is especially clearly manifested in cats. Becoming a mother, she almost forgets about its existence, devoting all his spare time caring for the kids.
This is not surprising because the kittens are born deaf, blind and completely helpless. And that Mama-cat is the responsibility to care for them. One of the main components of the care of offspring is feeding. Newborn kittens are not deprived of the sense of smell and can find the nipple.
The owner must ensure that all kittens have gained weight, because if they got a lot, a cat is very hard to take care of them and she may not have enough milk.