Don’t panic! Give Mama Cat a chance to come back.
Cats are excellent mothers and very devoted to their kittens. They do leave them alone for several hours a day to hunt, and sometimes they will move their litters to a new location. Back off to a distance of at least 35 feet and watch for several hours to see if the mother cat returns. Be patient. Healthy kittens can survive just fine during this period as long as they are warm. The biggest mistake people make is taking neonatal (ages 1-4 weeks) kittens away from their mothers.
Mama cat offers the kittens the best chance for survival, and her milk is the best food for the kittens. If she returns and the area is relatively safe, leave the kittens alone with mom until they are weaned. You can offer shelter and regular meals to mom, but keep them at a distance from each other. The mother cat will not accept shelter if the food is too close by, because she will not want to attract other cats near her nest.
Once the kittens are old enough to be weaned (around 6-7 weeks), they are ready to be socialized and adopted. Do not forget to have mama cat spayed, or this same problem will occur again soon! Female cats can become pregnant again even while they are still nursing.
If you discover that the mother cat has been hurt or injured and cannot care for the kittens, then you have to decide if you are able to care for the kittens. Think about the following things:
Do you have time do it right? If you do decide that the kittens need to be taken in, think about how much time you have to care for them. Kittens younger than four weeks require round the clock care, so know that by taking them in, you are putting them in a critical situation. They have to be fed every few hours, and they need manual help eliminating (pooping and peeing). Mama cat does this by grooming the kittens regularly, so you will need to do the same – likely with a towel or q-tip. Do a gut check and be sure you are up to this task. Do not assume that a vet or shelter will be able to do this for you. It is unlikely that you will find an organization with available staff or volunteers to take on bottle-feeding on short notice, and most of these facilities do not have someone on the clock to care for the animals 24 hours a day.
Can you get the kitten spayed or neutered? If you take them in, then you will be responsible for having the kittens altered when they are old enough to prevent them from producing even more homeless kittens. They will also need vaccinations, deworming, and possibly other veterinary services. Can you afford all of that?
Can you get the kittens adopted? Unless you plan to keep all of the kittens, you will need to find them new homes. Are you willing and able to put in the time and effort it will take?
We understand that you care a lot about animals and want to do what’s best for the kittens, but more often than not, people end up taking in a very young kitten without realizing how much care they will need, and end up leaving them on the doorstep of a local shelter or vet after a few days. The hard and fast rule is that if you are not truly prepared (both mentally and financially) to care for the pet, then you should not take it in.