A female kangaroo is pregnant for 21 to 38 days, and she can give birth to up to four offspring at one time, though this is unusual.
At birth, the baby, called a joey, can be as small as a grain of rice, or as big as a bee, at 0.2 to 0.9 inches (5 to 25 millimeters), according to the San Diego Zoo. When the joey is born, it is guided safely into the comfy pouch, where it gestates for another 120 to 450 days.
Inside the pouch, the joey is protected and can feed by nursing from its mother's nipples. Joeys urinate and defecate in the mother's pouch. The lining of the pouch absorbs some of the mess, but occasionally the mother will need to clean it out, which she does by inserting her long snout into the pouch and using her tongue to remove the contents. A young joey will remain attached to a nipple while the mother does this, but any older ones will be temporarily kicked out.
Another interesting fact about the mother kangaroo is that she is able to suckle two joeys at different developmental stages at the same time with milk that has different nutritional content, the New York Times has reported.
Joeys grow quickly, though, and at 14 to 20 months for females or 2 to 4 years for males, they will be fully matured.