A newborn kangaroo is less than 2cm 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. It has powerful front legs, though tiny, and it uses these to claw its way up, clinging to the mother’s fur. 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.