Chapter 577 - Kangaroo

Newborn kangaroos, also known as joeys, can apparently be as small as a grain of rice... We're talking anywhere between 0.5 cm and 2.5 cm. Once they're born, they first have to crawl their way into the safety of their mother's pouches.

And yes, the joeys do do their business inside their mother's pouch which needs to be cleaned regularly.