It does not sound good for your little one. I would get him to a vet like Debbie suggested ... a.s.a.p. and be prepaired for the worst.
When a momma chin rejects a kit, usually she knows there is something wrong with it that will cause it to soon pass away. Mother nature gives this blessing/curse to most wild animals. Usually, but not always, this is the reason she will reject it ... most of the time she is correct, but I have been able to pull a few (very few) through with supplemental feedings and care.
As far as you trying to take over for mom ...
Please read: "
The First Signs Of Trouble" at:
http://www.geocities.com/jobernstein1949/CAUTION: Some moms that have rejected a little one, due to injury or illness, and know they will probably die, will often just keep moving away from it ... BUT ... some will go ahead and kill it ... not out of cruelty, but to keep it from having to suffer. Sooo ... if you are already feeding it and mom has rejected it ... you might want to house it separately ... keep it warm and fed ... hold it, love it, but be prepaired to have to say good bye. This is the hardest part of being a breeder.
Please keep us posted.
Jo Ann