When did Mary and Joseph realize that Jesus was missing?

I know, I know what you mean.

Luke 2:44 states that the parents had covered "a day's distance" before they noticed Jesus was missing.

Explanation: Back in those days they travelled in groups with relatives and acquaintances. Joseph and Mary may have had other sons and daughters (perhaps six or more)(younger than Jesus; Jesus was 12) If the parents were busy with their younger children, and thinking perhaps that Jesus was with another group of the relatives; it could happen. At the end of the day, when the whole caravan stopped all in one spot each family did their headcount. They could not locate Jesus.

Luke 2:44 (God's Word Translation) "They thought that he was with the others who were traveling with them. After traveling for a day, they started to look for him among their relatives and friends."

After three days, they found him in the temple, talking about spiritual things with the older ones. Parents were obviously upset, for they said: "Son, why have you done this to us? Your father and I have been worried sick looking for you!"