What are baby koalas called?

A young koala is called a joey. It is not a "cub", as the koala is not a bear. Koalas are marsupials, and share the offspring name of "joey" with all other Australian marsupials, including all members of the kangaroo family, along with the wombat, quoll, possum, Tasmanian devil numbat, bilby etc, just to name a few.