Now his parents went to Jerusalem every year at the Feast of the Passover, and when he was twelve years old, they went up to Jerusalem after the custom to the feast. And when they had fulfilled the days, as they returned, the child Jesus tarried behind in Jerusalem. And Joseph and his mother knew not that he tarried, but they, supposing him to have been in the company, went a day’s journey, and they sought him among his kindred and acquaintance. And when they found him not, they turned back again to Jerusalem, seeking him.
And it came to pass after three days they found him in the temple, sitting in the midst of the doctors, and they were hearing him and asking him questions. And all who heard him were astonished at his understanding and answers. And when his parents saw him, they were amazed. And his mother said unto him, Son, why have you thus dealt with us? Behold, your father and I have sought you sorrowing. And he said unto them, Why is it that you sought me? Did you not know that I must be about my Father’s business? And they understood not the saying which he spoke unto them. And he went down with them and came to Nazareth, and was subject unto them. And his mother kept all these sayings in her heart. And Jesus increased in wisdom and stature, and in favor with God and man.
Source: Luke 3:1-2