Luke 2:43 in the World English Bible
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,
Context
42 And when he was twelve years old, they went up to Jerusalem after the custom of the feast.
43 And when they had fulfilled the days, as they returned, the child Jesus tarried behind in Jerusalem; and Joseph and his mother knew not of it.
44 But they, supposing him to have been in the company, went a day’s journey; and they sought him among their kinsfolk and acquaintance.