The Gospel reading at Mass (Luke 2:41-52) was the story of the 12-year-old Jesus in the temple:
Each year Jesus’ parents went to Jerusalem for the feast of Passover, and when he was twelve years old, they went up according to festival custom.
After they had completed its days, as they were returning, the boy Jesus remained behind in Jerusalem, but his parents did not know it. Thinking that he was in the caravan, they journeyed for a day and looked for him among their relatives and acquaintances, but not finding him, they returned to Jerusalem to look for him.
After three days they found him in the temple, sitting in the midst of the teachers, listening to them and asking them questions, and all who heard him were astounded at his understanding and his answers.
When his parents saw him, they were astonished, and his mother said to him, “Son, why have you done this to us? Your father and I have been looking for you with great anxiety.”
And he said to them, “Why were you looking for me? Did you not know that I must be in my Father’s house?"
But they did not understand what he said to them. He went down with them and came to Nazareth, and was obedient to them; and his mother kept all these things in her heart.
And Jesus advanced in wisdom and age and favor before God and man.