A lot of times (usually more in the wild) a animal parent, especially a mother, will notice if there is something wrong with one of her offspring (they could be sick, or be the runt, etc.) When this happens, the mother will push the one away so she can focus on the care for the others who will be more likely to survive. This does not happen too often with domestic animals, but still does happen. You need to take the kitten to the vet and care for it yourself. Feed it by syringe (they sell kits for that type of care at Petco). Also, at many animal shelters, they have people who foster kittens and puppies that are too young to be adopted out and for whatever reason are separated from their parents. Call around to shelters and see if they have people who do this. Explain your situation and they will most likely try to get you in contact with people who care for these kinds of animals everyday. Good luck
If it has been touched or played with by someone else maybe that's why. But i think you can feed it if you get syringe any kind suck up milk with it and let the kitten drink push it slowly. I tried it and all the cats i had grew up. But it might not bad enough.
I just think that some female animals are not the motherly type and don't care to be. ( Just like humans.) My female lab was a horrible mother but she was the best dog I ever had. You should probably have your mama cat spayed to avoid another litter.
If you touched the baby as soon as it was born with bare hands, no towel or gloves then the mother will reject the baby as you've touched it and it will smell of human and the cat will just take care of a baby as it should. If the kitten is still young, get a syringe without the needle, make sure the s is cleaned and put some milk in, put some on your kittens lip and let it lick it off, then slowly keep putting a little amount of milk in the cats mouth