If possible, bring the mother cat and kittens indoors, where they'll be safe. Confine them in a small room or a large cage in your basement or garage. Provide food and water for the mom and let her take care of the kittens until they're weaned, or ready to start eating regular cat food.
If the kittens have been orphaned, they will need a lot more help from you. Bring them inside and check their condition. They should be alert and warm to the touch. If they're cold and listless, warm them up right away. Put the kittens in a box or pet carrier with a heating pad set on low. Put a towel over the heating pad and make sure the pad covers only half of the bottom of the box.
The kittens must be able to move off the pad if they get too warm. Don't try to feed them until they warm up. It's dangerous for kittens to eat when they're chilled.
Kittens typically start to eat regular canned or dry food when they're four to five weeks old. Younger kittens have to be bottle- fed. Don't use cows' milk -- it causes diarrhea, which can lead to severe dehydration.
To prepare the bottle, pierce the nipple with a pin or slit it with a razor. Test the formula on your wrist -- it should be lukewarm.
Kittens less than four weeks old also need help with elimination, a job that a paws-on mom cat would normally perform. You should encourage them to urinate and defecate after feedings by gently swabbing the anal region with moistened washcloth or tissue, and by rubbing their stomachs.
They should also be burped after each feeding; hold the kitten against your shoulder and gently massage its back.
Caring for orphaned kittens is no small job, but it can be a lifesaving labor of love. Many extremely young kittens that end up in animal shelters have to be euthanized.
The average shelter simply doesn't have the staff and resources to care for kittens that must be bottle-fed 24 hours a day. Your help may be the kittens' best hope for surviving until they are old enough to be altered and adopted.