Male chins are able to breed at the tender age of 8-10 weeks old.  Females are not fertile until about 6-8 months old, although some breeders have had the odd female that became pregnant at the age of 4 months.  It's definitely better to have the females wait until they are at least eight months and older if possible, this gives them time to mature and achieve their maximum growth, especially in the pelvic region.  Gestation is about 111 days from the day of mating, give or take a day or two.  A litter can be one or up to six chins, but usually is one to two babies.  Babies usually arrive in the wee hours of the morning but at times will appear later in the day.  A mum chin will labor for about an hour to an hour and a half with a baby and afterward clean the baby and dry it underneath her.  If she has more than one baby it may be necessary for the breeder to interfere here and dry the first baby if she leaves it to move about the cage in her labor.  A metal nest box then is a handy thing then if you can mount a heating pad under it to keep babies warm while mom is out of the cage.  Mom will also appreciate the warmth while pregnant too.  Females also have two uteruses and will go into estrus immediately after birth so it may be necessary to remove the male a day or two before she delivers but keep him close in a nearby cage if you wish to prevent a breedback.  He can be returned then after about 72 hours and will help out immensely with the babies.  Afterward the babies will be well taken care of by both mom and dad and will be ready to be weaned at about 8 weeks old.  Average sized babies are anywhere from 25 grams to 60 grams and of course bigger is always better and gives them a better chance of survival.   They will start eating pellets and hay at about two weeks old, and are able to run about the cage from day one.  As cute as the adults are, babies are cute enough to die for.   The greatest danger at this time is for the babies to get out of the cage and become chilled which is deadly, so care must be taken to somehow enclose the holes in the cage if they are larger than 1/2 inch by 1 inch.   We have used gutter screening to wrap around the bottom 4 inches of the cages to prevent the more persistent escapees.   At about eight weeks the babies are weaned and the males are removed from the cage to prevent impregnating mum, females can remain with mom until at least six months as long as dad is not also present.  We like to keep babies for a week or so after weaning just to make sure that they are eating well and not overeating, which can cause diarrhea.  But then they can go to their new homes.