The "three days" covers one day of traveling away from Jerusalem (before Mary and Joseph knew that Jesus was missing), another day retracing their steps, and a third day in Jersualem looking for him.
Note that when they find him, he is depicted as a "learner." He is "listening" to teachers and asking them questions. One of the apocryphal gospels (the Gospel of Thomas) projects the popular image of Jesus turning the tables and acting as a teacher.
The teachers (and spectators) recognize that Jesus is well-trained in the Jewish scriptures and traditions. There is no need to think of this as miraculous knowledge. Jesus is truly divine and truly human - like us in all things but sin - and he had to learn just as any youngster has to learn.
Which means that Mary and Joseph deserve credit for his religious education.
Who deserves credit for teaching you about God, amd about our religious traditions? Not just teaching you facts, but helping you to feel at home with God and with our traditions?
There are probably a fair number of people on your list, some who played a major role, some a minor one. Who are the one who had the biggest effect?
They deserve a prayer or two ... of thanks.
- Little Blue Book, Diocese of Saginaw