These are to be found in Luke 2: 49.
At the age of 12, Jesus was taken from Nazareth to the Temple in Jerusalem but Mary and Joseph lost him in the crowds there. When he was found, they saw that he was talking to the teachers there, amazing them by his answers. When Mary questioned him saying that they had been worried about where he was, he replied:
"Why were you searching for me? Did you not know that I must be in my Father's house?"