Luke 2:45

and when they had fulfilled the days, as they were returning, the boy Jesus stayed behind in Jerusalem. Joseph and his mother didn't know it,

but supposing him to be in the company, they went a day's journey, and they looked for him among their relatives and acquaintances.

It happened after three days they found him in the temple, sitting in the midst of the teachers, both listening to them, and asking them questions.

All who heard him were amazed at his understanding and his answers.