Growing up means leaving home a little at a time. A newborn kangaroo is only about the size of a jellybean, and it crawls into its mother's pouch by itself. As the joey grows, it starts to hop out and explore, going farther and for longer each month. It hops back in to stay safe, and it keeps drinking its mother's milk until it is about 10 to 12 months old.

Songbird chicks come out of the egg helpless, with their eyes closed and almost no feathers. They stay in the nest and wait for their parents to bring them food. A fledgling is a young bird that has left the nest but cannot yet fly well. If you see one hopping on the ground, it is usually fine, because its parents are close by and feeding it. The best thing to do is leave it alone.

A giant panda cub is born pink and blind, and its mother holds it close to her chest. In the first weeks she will not leave it, even to eat or drink. The cub cannot move around much until it is about three months old. By three to five months it walks pretty well. At five to six months it starts to try eating bamboo, but it keeps drinking its mother's milk long after that.

A black bear cub is born in the den in the middle of winter, while its mother is asleep there, and it weighs less than a pound. The cubs drink their mother's milk all winter, and by spring they weigh about 5 to 7 pounds. They stay with her through their first summer and den with her again the next winter.

A blue whale calf drinks very rich milk, and it can gain well over 100 pounds in a day. A nursing whale mother can make 50 gallons or more of milk in a day. A humpback whale calf stays close to its mother for about a year. Then it is weaned and goes off on its own.

A mother sea turtle does not stay to care for her eggs. She goes back to the sea, and by the time the hatchlings come out of the nest at night, she is gone. The hatchlings find the sea by the slope of the beach and by the moon or starlight on the water. After they reach the water, they swim out to the open ocean, where they live for several years. Many years later, a grown female usually returns to lay her own eggs near where she hatched.

Frogs take their own time. Most frogs come out of eggs as tadpoles, and bullfrog tadpoles may take several years to turn into frogs. As a tadpole changes into a frog, it grows lungs and loses its gills, so it can breathe air. A young frog still has a stump of a tail when it first comes out of the water, but the stump soon disappears.

Words to know

• fledgling: young bird
• weaned: no more milk
• hatchlings: newly hatched babies
• nursing: feeding milk