Usually, kittens should be cared for by their mother until they are at least 6-8 weeks old. However, if the mother cat cannot care for her baby (sick, dead, abandoned), then please refer to How to Raise a Newborn Cat After Losing Mother.
Maintain temperature
You need to maintain a warm temperature for kittens because their body temperature is lower than that of an adult cat. If the temperature cannot be maintained, it is likely to cause some adverse effects on their health. If your kitty is cold and needs immediate warmth, place them in clothing so that their body is against your skin to warm up faster.
Prepare a very warm bed for kittens so they feel like they are in their mother's arms.
Or you can refer to the following temperature-controlled heating cages for cats:
Feeding the cat - milking phase
Cats are intolerant of lactose and milk, as milk can disrupt their digestive system and cause discomfort, diarrhea, or flatulence. So look for recipes made specifically for kittens.
Before feeding, make sure the bottle has been cleaned and sterilized with 45-degree warm water. Also, choose bottles with soft nipples and small nipples to ensure nursing kittens don't choke.
While feeding put the kitten on a towel or blanket. Remember not to put your cat on its back while feeding, as sucking can cause the cat to suffocate and increase the risk of pneumonia or even death.
If your kitten is not used to or has trouble handling the bottle, you should instead use a syringe or small syringe to push the food in.
If you see some milk left in your kitten's mouth and bubbles or small bubbles around the mouth, it's a good sign that your kitten's litter is full. You must make sure your kittens eat enough and don't overfeed them as this can cause diarrhea, discomfort, or other problems.
Feeding the cat - weaning stage
At about 4 weeks old, kittens will begin to learn to eat cat food and wean. At this point, you should give them kitten food mixed with boxed bolognese. Usually, by week 5, kittens can switch to wet food without issue. Also, alternate between wet and dry foods to make sure they stay hydrated.
How to clean a newborn cat that lost its mother
Newborn kittens need to get rid of waste from their bodies. Female cats will lick their kittens' genitals and surrounding areas to stimulate their bowels and bladder. You will need to use a warm, warm cotton pad or washcloth or a warm damp washcloth to facilitate the kitten's discharge. Gently stroke the kitten's belly. Make sure the area is clean and free of waste to protect the kitten's skin. When kittens are 4 weeks old and they can toilet on their own, you can start teaching them how to use the litter tray.
Raising a newborn cat that has lost its mother is no easy task. It takes time, attention, and a lot of care. However, with the above knowledge and guidance, hopefully, your kitty has a high chance of survival.