Marsupial
Marsupials have a special pouch where they carry their joeys. After the birth the joey goes into its mother's pouch, where it can drink milk and is kept warm and safe. When the joeys are young they stay in the pouch all the time, but when they are older they can leave it for short times. When they are old enough and too big for the pouch they do not go into their mother's pouch anymore.