I was a pre-Vet Tech at one of my last jobs.
First, ensure that the kitten has had its first bit of cholostrum (that is the first milk from the mother). You can go to any pet store and purchase kitten milk replacer, you will need that and a little bottle, it should be sold directly beside the milk.
As for the kitten, you need to get a fluffy warm blanket and preferably a heating lamp as compared to a heating pad. I've seen many casualties of baby animals due to heating pads getting far too warm. Heating lamps are much better.