This is called a litter, and the pups in a litter are called litter mates. Pups are born inside a den. A den is sometimes a small cave or a hole dug out of the ground. The den must be big enough for the mother and her pups. It shelters them from the weather and protects the pups from other animals that may want to hurt them.
Packs sometimes use the same den year after year.
At other times, they make or find a new den each year. Pups grow inside their mother for about 63 days before being born. At birth they weigh only one pound, and their eyes are closed. Pups grow quickly. About 12 to 15 days after they are born, they open their eyes.