If the mother guinea pig is present, you can leave the majority of the care for the babies to her. Guinea pig babies don't need much more than their mother's milk and warmth just after birth, and it's probably a good idea for you to allow her to take care of the immediate needs of her litter until the young are about five days old. If you happen to be caring for guinea pig babies that have been orphaned or aren't being taken care of by their mother, you will have to visit your local pet food store or vet's office to get a pet nurser and some formula to feed to them. The babies will need feedings roughly every two hours for about five days, and after that point, you probably can reduce their feedings to once every four hours.
There are some guinea pig babies that start eating solid food when they are very young, so you can offer small amounts of grass or hay to see if they start eating it when they are about two to three days old. Some pet food stores also sell pellets for guinea pigs, and you can give these to the babies as long as you soak them thoroughly so that they will be soft to chew on. There is no need to worry if your pets do not seem interested in the food immediately — they likely will eat it when they are ready.
Even though many people believe that you shouldn't touch baby guinea pigs soon after they are born, this isn't true. As long as you are gentle, you can handle the babies right away. Be careful to keep the babies in the cage with their mother as often as possible if she is present, because they need to be nursed frequently. When the babies are a few weeks old, it's typically considered acceptable to separate them from their mother for longer periods of time.
If you are caring for guinea pig babies that do not have a mother present, you should realize that they might not survive, even if you are providing regular feedings and round-the-clock care. The majority of guinea pig babies are not able to live without their mother's milk, and there's a good chance that you might lose most of the litter for which you are caring. This could be frustrating, because nursing infant guinea pigs is a full-time job considering the frequency of the feedings. Some of the litter, however, is likely to survive if you are doing your best. Try to get a close friend or relative to alternate feeding times with you for the first week or so to keep you from becoming exhausted.