If you have found tiny kittens alone without a mother, here is detailed help on how to care for them at the following website:http://www.kittenrescue.org/pages.php?pageid=15
However, mother kittens do leave the nest from time-to-time to find something to eat or to eliminate, and are sometimes gone for even 2 or three hours (depending upon how easy it is for them to find food safely). So don't automatically assume all kittens found alone have no living mother. Do keep an eye out for a possible mother cat, but do not leave the infant kittens for long without intervening in case there is no mother cat coming back. The mother will not come back to the kittens with you standing by them, so stay a distance away and as out of site as possible while keeping a watch for the mother to return.
Keeping a tiny kitten warm is the most essential thing. Kittens under three weeks old cannot regulate their body temperature. The kitten must be warm before offering it anything to drink. Cold kittens cannot digest food.
Kittens have trouble digesting cold liquids, so along with keeping the kittens warm, warm the formula you give them to drink. Test it on your wrist to make sure it is not hot.
If putting the kitten in a box with a heating pad, put the heating pad under the box. Be sure it is not set too high, and also there must be an area with no heating pad so if the kitten feels too hot, it can wriggle over to where it is cooler.
Have a blanket or towel smooshed into a little nest shape, with raised up edges, so the kitten can snuggle into it, rather than a neat, flat lining the bottom of the box. Just a flat lining won't help keep the kitten warm. Put a small stuffed animal in the box so the kitten can snuggle with it. That will help it keep warm, and may also help make the kitten feel like a littermate may be there, sort of.
Cows milk does not supply needed nutrients for kittens. The best thing to feed tiny kittens is KMR (Kitten Milk Replacer). You can get it at many stores such as pet stores, and even most local grocery stores and Wal-Mart. If you cannot get to a store at the time you found the tiny kitten, you can make an emergency formula. The following formula is "Formula #2" from www.kittenrescue.org
.Emergency Kitten Formula
8 ounces homogenized whole milk
2 egg yolks (do not use the egg whites!)
1 teaspoon salad oil
1 drop liquid pediatric vitamins (optional)
The formula, whether it is KMR or the Emergency Kitten Formula, must never be served cold. It must be feed warm. You can warm it to a safe temperature by putting the bottle filled with it in a pot or bowl of very warm water for a few minutes. Then test it by squeezing some onto your wrist. Do not microwave the bottle or formula to heat it up. You don't want it "cooked" or to get unevenly hot. In addition, a bottle in the microwave will explode.
You will also need a pet bottle if the kitten is very tiny. Those same stores that sell KMR would also have the pet bottle. Do note that the nipples don't come with a hole cut out, for some reason, so you must carefully make a small hole.
If you can't get to a store to get a bottle, you can use a clean syringe or eyedropper to carefully drip a drop at a time into the kitten's mouth. If you don't have those items, you can use a spoon to most carefully slide a tiny bit at a time into the kitten's mouth. Great care must be taken not to put too much formula in at a time, or the kitten may choke or inhale it into the lungs.
Never feed a kitten with the kitten held upside down, feet up. The kitten can choke or inhale the formula into it's lungs in that position. Set the kitten with it's feet towards the floor, or slighty elevated in the front, replicating the position a kitten would take if nursing on it's mother.
Kittens under 3 or 4 weeks old cannot eliminate on their own. They need their rear ends stimulated, as if a mother cat was licking the area. You can use a warm, damp washcloth or damp tissues to do that. Use firm strokes, but take care to not rub hard, or you will irritate the delicate skin. Do it a few times a day, and about an hour after feeding.
Do take the kitten to the vet as soon as you are able to.Be sure to read the articles on caring for orphan kittens very carefully, and not just this post. There is much more detailed information you need to know than in this post.
Also read the following articles on caring for orphaned kittens:http://www.hdw-inc.com/tinykitten.htmhttp://cats.about.com/cs/kittencare/ht/bottlefeed.htmhttp://www.feralcat.com/raising.html