I woke up this morning to find 2 baby guinea pigs with the 2 older ones I already had. I had thought the 2 older ones were both female, but unfortunately one is a male. There's no denying it's the father either, because one of them looks exactly like it and both have the same type of fur. I was surprised to learn that baby guinea pigs are born with their fur and their eyes open, unlike other rodents like rats and mice. The babies are pretty much ready to go once they're born.