Ones that are conceived at a different time rarely have a chance to make it and/or if the mom does not have enough milk to support all the kits, she will abandon the smallest/weakest one, so that the others may survive on what she has. Also, those conceived at a different time are usually not fully developed yet. It is called superfoetation, below is a picture of a male and female kit, born in the same litter. (Just click on the picture to enlarge it.) The female kit only weighed 18 grams, the male weighed 54 grams. I have helped a few through the rough part ... some survived, some did not. This is the down side of breeding.
If you can find some raspberry leaves, this will help her milk come in better ... if that is the problem. A vitamin C tablet will help with extra vitamins and Alfalfa hay is richer in nutrients than the Timothy hay. I usually keep my females on it when in breeding and while they nurse. Also Nutri-Cal is good to boost her needs for extra calories and nutrients at this time.
Goat's milk is the best if you want to attempt to feed the little kit. Goat's milk mixed 1/2 and1/2 with warm water and fed with a glass eye dropper works best for me and my little ones. Wrap the kit in a clean wash cloth like a papoose and hold at a 45 to 50 degree angle. Have a damp cloth ready to clean it's face and chin constantly ... if the formula dries, it will take fur and all off to clean it. Q-Tips are great to help control the drips. Only put one drop on the kit's lips at a time ... do not put the dropper inside the mouth, event rhough they are tiny, their suckling ability will astound you. They can suck the dropper straight through to the throat in a split second. He will need to be feed about every 2 hours for the first two days. (I've napped in a chair for days in my chin room many a time. This is all part of being a breeder.)
Please keep us posted on the new chin family's progress.
Jo Ann