There's a really good book I read in college called Jesus: An Interview Across Time that delves into this question. It's a work of fiction and the author is a psychologist...his premise is that Jesus didn't know He was God from birth, but learned it over time. Like /u/TheChickening said, we can't tell...and by no means am I recommending this book as a replacement for Scripture...but it was an interesting take, and made Jesus seem somehow more human to me.