Most marsupials have pouches where the tiny newborns develop. A koala mother usually gives birth to one joey at a time. A newborn koala is only the size of a jelly bean. Called a joey, the baby is blind, naked, and earless. As soon as it's born, this tiny creature makes its way from the birth canal to its mother's pouch. Using the two well-developed senses it's born with—smell and touch—along with its strong front legs and claws and an instinct that tells it which direction to head, the baby koala reaches the pouch. There it stays, safely tucked away, growing and developing for about seven months.
After a baby has been in the pouch for about six months, its mother begins to produce a special substance called pap. The joey feeds on this in addition to the milk it's already getting. Pap comes from the mother's intestines and contains bacteria that the joey needs to have in its own intestines so that it can digest an adult diet of eucalyptus leaves.
At about seven months, the joey leaves the pouch to eat leaves, but returns to it to nurse. By the time the joey is about one year old, it stops nursing and eats just leaves.