When Jesus was 12 years old, Joseph and Mary found Him in the temple, talking and asking questions with the teachers there.
He was actually learning more about who He was.
Jesus was not born with an automatic understanding that He was the Christ. He learned about himself through the scriptures.
The Father planned it that way. We ALL have to find out who we are, by reading and understanding the Word of God. That is how we discover what God has called us to be.