Which animal grows the maximum from birth to adulthood? Though a male kangaroo can be about 7 ft. tall and weigh 90 kg, at birth they are about 2 cm tall and weigh a few grams only! After birth, the baby has to climb about 6 inches along the furs of its mother’s abdomen to reach the edge of the pouch and enter into it. It is equivalent to a human baby climbing about 10 ft.! The infant kangaroo is suckled inside its mother’s pouch, where it completes its development to emerge when it weighs more than a kg.