The term for a baby kangaroo is joey. A male kangaroo is referred to as a boomer, and a female kangaroo is called a flyer.
Interestingly, the name kangaroo arose from a misunderstanding during a conversation. A European explorer, curious to know the name of the large, strange-looking animals, inquired of an Aborigine. Apparently, the Aborigine was unsure of what the European was asking and replied in his native tongue that he did not understand. The word the Aborigine used, kangaroo, was taken by the explorer to be the name of the animal. This has remained the name for the largest species of the hopping marsupial, as smaller kangaroos are known as wallabies.