The Church may teach (I haven't looked for a definitive articulation, but I've seen it asserted by a number of bloggers) that Jesus knew from the moment of His birth that He was God. How this reconciles with "like us in all things but sin," is an interesting question--a question addressed by Anne Rice in her wonderful Jesus the Christ: Out of Egypt.
If I must accept on faith that Jesus always knew His divinity and that He was like us in all things but sin, I'm left to wonder how these two partially antithetical tenets are resolved. Anne Rice explains it superbly--while we may know, sometimes we do not understand.
As babies, I suppose there is a rudimentary "knowledge" that one is alive and one is human. Can a baby be said to understand what it means to be human? As one cannot inquire into the understanding of a infant, one cannot speak definitively; however, it is on the very far side of probability that any infant truly understands his or her condition.
I think now about the babe in the manger. This infant who was God possessed the mind and the physical limitations of the human being in the human body. He was to undergo ontogeny--growth in understanding and in being. That is the path of all of humanity. It is important that He should do so, for to do anything else would not be fully human, and Jesus came to bear the full weight of humanity. Jesus may have known that He was God, but if He was fully Human, it took Him some time to fully comprehend what that means.
Think for a moment of being the mother of this very special child. What a responsibility, what a privilege. You are charged with bringing God to an understanding of His Godhood. It is principally through your love, care, and nurturing that this Child will come to understand what it means to love, what it means to be human. And from the foster-father of this child will come the knowledge of what it means to be a man and what it means to love like a man and worship God as a man.
This child, who knew from the moment of His birth that He was God was trusted to two parents who were to help Him understand what this great mystery meant.
In the same way, we come to understand our human condition from our own parents. This means that some of us understand some aspects of it better than others. Depending on our parents, we may be more inclined to "head" thinking or "heart" thinking, or to some ideal balance between the two. Depending on our parents we will understand to a greater or lesser degree our interdependence and our common lot with the remainder of humanity.
But it is up to the working of the Holy Spirit and the Father in heaven to help us understand how Christ lives within us and what that means. When we stand by the creche this Christmas, we do well to bring to mind, that we are not even yet as that Babe in eternity. This earthly life is our gestation, our maturity for our ultimate "Christmas," our individual nativities in eternity--to be greeted by the Father who has waited so long to see us born into that life. Angels rejoice and Saints sing praises as we enter that life. And should we share in that life as we live in this passing world, O, how much better for all of those around us--what a blessing to them and to the entire world.