Here's why:
* Koala babies are called joeys. They are born very small, about the size of a jellybean!
* Joeys stay in their mother's pouch for about 6 months. During this time, they grow a lot and start to resemble miniature koalas.
* Even at 6 months, a joey is still quite small but much larger than a mouse. They are about the size of a kitten.
So, while baby koalas are tiny, they are definitely bigger than a mouse.