Around the age of four or five the female polar bear can start having babies. They usually only have two cubs and they have these babies in a cave they’ve dug in a large snow drift. They stay there over winter and come out in spring with the babies. The babies are much smaller than human babies when they’re born. They are the size of a rat and weigh little more than a pound. They can grow to full man size in a year if they have lots of food.