So I imagine the conversation between Mary and Joseph went like this:

What do you mean he's not with the caravan?Where could he be?

I thought he was with you.

Well, I thought you knew where he was.

How could this happen? How could he do this to us?

He's still in Jerusalem? Why would he do that?

My baby is in the city? What if something has happened to him? He could have been taken and sold into slavery. He could be on his way to ...

Wait till I get my hands on him...he'll be grounded for life.

I'm sure he's fine...he's very mature for his age. You'll see. He's probably having the time of his life.

Yes, well, he'd better live it up now because when I catch up with him...

Fear and anger and a whole set of what-if's must have flashed through their minds as they set out to return to Jerusalem. The city was not a place for an adolescent to be alone. Especially not this pre-teen. Since his birth, Mary had been waiting for something. Parenting Jesus was like waiting for the other shoe to drop. You can give birth to such a special child without wondering why, how, when, what. For years, she had watched him grow and wonder what God had in store for him, for them. Was this part of His plan? This disappearing? Had Jesus run away? Sometimes she thought she didn't even know her own son.

She should have seen this coming. After all, wasn't he almost a man. When she was his age, well, a year or so older, an angel had told her she would be a mother. Why couldn't that angle have stuck around for times like this?
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So why did it take three days of searching to find him? Did they have to retrace their steps through the whole city? Why as the temple the last place they looked, instead of the first place? Did they think he'd be in prison? In the marketplace? In the synagogue school? I think I'd have thought: "We always come to the temple. Every year to the same place, so that's where he'll be."

But it still took them three days to find him. Why three days?

Could it be a foreshadowing of the three days in the tomb?

When they found him, he was listening and asking questions. Not teaching, but encouraging others to answer his questions. How had this carpenter's child astonished the religious leaders and amazed his own parents? Why did none of them request the boy be left there? Didn't Solomon's mother give him to the priests to raise when he was only a toddler? Surely there was a school there and Jesus was old enough to have been left there. If he were that smart, why not leave him to be trained as a priest?

Or did the prejudices of the priests prevent this (Nothing good can come out of Nazareth)? Or perhaps they didn't want to deal with a pre-teen who knew more about the Scriptures than they did.

Or perhaps it wasn't God's time yet and Jesus knew and understood that. "He went down to Nazareth and was subject to them (his parents)." There was much to be learned in obedience, in serving, in learning from his father and his mother. "And Jesus increased in wisdom and stature, and in favor with God and men."

At 12, he thought he was ready. But after three days, he understood he needed to grow and mature more. He needed to do that within the shelter of his family and his relationship with his parents. They cared enough to search for him, but also perhaps to give him 3 days' taste of freedom.