Children acquire language quickly, easily, and without effort or formal teaching. It happens automatically, whether their parents try to teach them or not.
Although parents or other caretakers don't teach their children to speak, they do perform an important role by talking to their children. Children who are never spoken to will not acquire language. And the language must be used for interaction with the child; for example, a child who regularly hears language on the TV or radio but nowhere else will not learn to talk.