Beavers mate during the winter, from January to March. Baby beavers are called kits. The basic units of beaver social organization are families consisting of an adult male and adult female in a monogamous pair and their kits and yearlings.^[5] Beaver families can have as many as ten members in addition to the monogamous pair. Groups this size or close to this size build more lodges to live in while smaller families usually need only one. At around 2 years of age, the kits leave the lodge and make one of their own. At 3 years, they find a monogamous mate. 

When young are born, they spend their first month in the lodge and their mother is the primary caretaker while their father maintains the territory. In the time after they leave the lodge for the first time, yearlings will help their parents build food caches in the fall and repair dams and lodges. American beaver kits can swim 24 hours after birth.