Smallest New Bron Kangaroo . . .

A newborn kangaroo is less than 2 cm in length (less than an inch) when born and weighs about half a gram. It is about the size of a kidney bean. 

A baby kangaroo (joey) when born is a blind, hairless embryo that makes it way from the birth canal of the mother kangaroo up to and into the mother's pouch. The joey then latches onto a teat inside the pouch, which then swells inside mouth of the joey, basically securing it from falling or being jolted from the pouch.

The joey then continues to form and grow.

The mother kangaroo can have two joeys of different ages in a pouch, at the same time. When this occurs, the mother actually gives two different milks for each joey, according to its nutritional needs. At the same time, she may have an older, almost -weaned joey, which requires a third milk. The more mature joey will leave the pouch as a fully formed animal with sight and fur and able to move around, a little less than half the height of the mother kangaroo. It will quickly return to the pouch when it is scared, tired or in need of security, until the mother deems it weaned and evicts it permanently.