Ideally when breeding you will want to breed a couple of does around the same time so if one fails in her duty to care for her babies, you can foster these babies to the other mom. This doesn’t always work out though. If you live close to another breeder you can call them up to see if they have any compatible litters to foster to. It’s always worth a try. Try to keep the age gap no greater than 5-7 days as a lot of growing takes place this first week.
Reasons for fostering babies from birth:
Kits over the age of 3 weeks can sometimes wean early (though not recommended.) This usually should only happen without a foster mom after the death of the mother. I would still suggest supplementing them with goat or kitten milk.
You can successfully use kitten milk or iron free baby formula (baby formula has to be diluted more.)
Use eye droppers to feed the babies. You will have to feed them every 3-4 hours. A mom rabbit only feeds her babies once a day but is able to feed them much more than you can with the dropper in the same amount of time. The reasoning behind this is that it’s very time consuming (especially with multiple babies) in addition to the dropper being a poor substitute for what nature has perfected.
Once they turn 10 days old you can cut feeds down to 4 times a day and start providing hay and oats to chew on. In another week, rabbit pellets may be introduced.
At the age of 4 weeks, they can now be fed once a day and are mostly depending on pellets, oats, hay and water provided.
I have heard of some people using baby food high in protein to foster babies. I have not had the opportunity to test this since I typically breed 5-10 does a day to make sure if needed that I have enough foster moms!