Tabby was barely out in the world before she began nursing from her mother. Vulnerable newborn kittens spend their first two weeks nursing and sleeping. During this time, their hearing and sight develop and their sense of smell is fine-tuned. Mama's milk plays a vital role in their healthy development. Milk from your fridge or from any source other than Mama Kitty is off-limits.
There's little rest for a mother cat during the birthing process. Depending on how many kittens she's delivering, the ordeal can take as little as an hour or two, or may stretch an entire day. When she delivers a kitten, the cat gets busy cleaning her new baby, freeing the baby of his amniotic sac and chewing off the umbilical cord. When those basics are taken care of, Mama will begin nursing her newborn kitten. The mother will go through the same process for each kitten; by the end of the process, she'll be feeding the entire litter.
If Mama's healthy and nursing her new babies, there's no reason to step in and help her out. There's nothing you can give Tabby and her littermates that will improve what they're getting from mom. In fact, you should avoid touching them at all for a week or two. For the first three or four weeks, mother's milk is what's best for them, providing the whole gang with all the nutrition they need. It's normal for newborn kittens to nurse about every one or two hours.
If mom's not healthy or in the picture, Tabby and her siblings will need nutrition right away, as they would naturally get from her mother. If you have feeding duty, you'll need to use a commercial formula for kittens and kitten bottles for feeding. Your vet, local animal shelter and pet store are resources for providing you with the right gear. If you're Tabby's first source of nutrition, she'll also need colostrum, the pre-milk fluid produced before birth. It's the first thing kittens eat and is rich in antibodies, protein and minerals. Mother cats naturally provide this substance during the first 24 hours they nurse their young. Plan on feeding newborn kittens every two to two and a half hours for the first week or two; by the time they're three weeks old, they'll need fed in two-and-a-half to three-and-a-half-hour intervals; at four weeks, they can eat every four to five hours.
Off the Bottle
Whether it's you or Mama Kittty doing the feeding, Tabby and siblings will start the weaning process around 4 weeks of age. Of course, they won't be ready to start living on cat food and water at 4 weeks, but the transition can start at this point. The best way to start the weaning process is to mix kitten food with milk replacement and water, making a gruel for the kittens to lick. Canned kitten food is easier to use than dry, as dry has to be ground up for easy eating. You can dab a bit on Tabby's paw or let her walk through the gruel and discover on her own that it's actually a tasty menu option. If Mama's around, she'll likely learn as much by mimicking Mama's eating behavior. When it's time to wean Tabby and siblings, avoid cow's milk. Cow and goat milk doesn't have sufficient protein and fat for kittens and can cause diarrhea and problems with Tabby's tummy. The same goes for cats of all ages.