Often times kittens are not abandoned at all. Just because the mother is not with them, does not mean she has left for good. She could be watching them from nearby, hunting for food, or she may be in the process of moving them to a new location. The best thing to do is to wait several hours and see if the mother returns. One thing is for sure, she will not return if you are hanging around, so watch from afar.
Young kittens are best off with their mother so it is best to leave them with their mother while they are nursing.
Newborn kittens must be kept warm and should not be fed when they are cold. You can keep your kitten in a box with soft bedding and use a heating pad or a microwavable heating disc under a portion of the bed. It is important that the entire bed is not heated so that the kitten can move away from the heat in case it gets too hot.
1 week old kitten: bottle feed every 2-3 hours.
2 week old kitten: bottle every 3 hours
3-4 week old kitten: bottle every 4 hours
4 week old kitten: bottle feed every 8 hours and begin encouraging eating gruel by combining wet cat food and formula. You should also give the kitten access to water at all times.
Some kittens quickly start eating gruel or dry food and other are reluctant to leave the bottle, each kitten is different. Some kittens insist on being bottle fed until 6 or 8 weeks old. To encourage your kitten to eat independlty you can leave dry kitten kibble and/or canned kitten food out all the time.