When Joseph and Mary started for home from Passover, the twelve year old Jesus intentionally remained behind in Jerusalem. They returned to find Him sitting among the teachers in the Temple amazing everyone with His questions and answers. His parents were also amazed, but not for the same reason. From Mary's words, it seems they were astonished that Jesus would do this to them. Christ asks why they were searching for Him. Did they not know where He would be and what He would be doing? This seems reasonable given the revelation they had already received.