The correct answer is "all these things contribute to childhood amnesia." This is because when we are born, our brain is still forming, so the information we receive cannot be organized correctly, we also do not have concepts or memories that allow us to understand what we perceive, that is why we can not understand it. As we grow our cerebral cortex matures and we acquire memories and concepts that allow us to organize what we see, and in this way form memories.
I hope my answer can help you.