Weaning kittens before 8 weeks of age will reduce their resistance to common feline viruses and add unnecessary stress to their digestive systems. Far to often, kittens are brought into the adoption center when they become a nuisance to the owner, not when they are ready for adoption. Kittens at 4 weeks of age become quite active and begin eating solid food, but this does not mean they are ready to leave mother's side. They are still receiving important antibodies through the mother's milk, and their digestive systems are still very immature. Most kittens turned into a shelter at this age will become ill or will fail to thrive. Many will die despite our best efforts. We ask owners of unplanned litters to keep them at home with mommy until 8 weeks of age. Kittens who receive their first kitten vaccination before entering the shelter will have an additional advantage in staying healthy (NHS)
If you cannot locate mom, do not leave orphan kittens outside alone as they will likely die.Many kittens found alone are not orphaned or abandoned by their mother. If the kittens are safe for the time being, you should observe the nest to see that the mother returns soon; observe quietly from a safe distance if dealing with a shy or feral mother. If needed provide them with warmth and a simple shelter. She could be off eating or in the process of moving them one by one to a new location. If she does come back, you will need to decide how best to help her situation and get her and her kittens to safety
As soon as you find an orphaned kitten or kittens it must be protected from becoming chilled. Place it under your clothes next to your skin. Most of the young kitten's energy is needed for growth and yelling for more food, so there's not a lot left over for heat generation. Normally the mother cat and litter mates would provide a good deal of warmth. During their first week, kittens should be kept between 88 and 92 degrees F. For the next 2 weeks they still need temperatures of 80 degrees or so. Never attempt to feed a chilled kitten.
As soon as possible, take the kitten to a veterinarian to be checked out for dehydration and general condition. Kittens can become dehydrated very quickly without a mom and may need fluids under the skin. Kittens that are dehydrated from lack of fluids or diarrhea will have very little energy or appetite, so this is important to take care of immediately. Abandoned kittens will need to be cleaned and rid of fleas soon after they are found. Flea anemia can hamper any attempt to save the kitten and fleas carry tape worm eggs. The vet will carry flea products suitable for use on kittens. Do not use commercial products on kittens as they can kill them.
When you get the kitten home you must find a place in your home that is safe, warm, draft-free and isolated. A heating pad set on low beneath HALF of the kittens bed will help to keep him warm and allow him to get off if he is to warm or being burned. Make sure and set the heating pad BELOW the box itself, to one side or corner under the nest box, so that the kittens can move to a cooler area inside their box if it becomes too warm for them.The kitten should always be able to crawl away from the heat source and protection should be provided in the form of towels or blankets to prevent thermal injury.