Mother cats are usually stoic and tough, often fully capable of raising their kittens without much if any human intervention. However, if you're around a mother cat and her kittens, it's always sensible to keep an eye on things such as frequency of feeding sessions or excessive crying. If anything seems off, call your veterinarian.
Once a mother cat is in labor, it's usually not long before she begins nursing her little ones. They typically start feeding between one and two hours after birth, sometimes even before all of their littermates have come out. These initial nursing sessions are important. The first breast milk that mother cats release is colostrum, a thick and smooth substance that contains antibodies that shield kittens from many early illnesses. This defense generally lasts six to eight weeks.
Neonatal kittens need lots of feeding from mom, so expect to see the queen nurse each two to three hours or so, and perhaps as often as every hour or two. As the little guys get a bit older, they don't need to eat as often. By the time kittens are 2 or 3 weeks old, they generally can feed in intervals of four to six hours. Once they're three or four weeks old, they typically can eating every six to eight hours. At this point, the tiny kittens are usually mature enough to start weaning and to begin consuming real "big boy" and "big girl" kitten foods.
Not all newborn kittens have their mothers around to nurture them. If you're looking after motherless kittens, it's your task to feed them commercial kitten formula. You'll need to bottle-feed these kittens just as often as other kittens are fed by their mothers. You also might need to bottle-feed if a mother cat is ill and can't lactate. Talk to your veterinarian if you have any concerns about the mom's health or feeding the litter.
End of Nursing
Nursing usually comes to an end when kittens are about 6 or 7 weeks old. Mother cats generally don't stop nursing on a dime. The process works pretty gradually, with the mothers eventually steering their youngsters into the direction of dining on "real" foods exclusively.