Deep questions from a three year old

Cole asked me the other night if he knew me when I was a kid. I told him, "no you didn't know me because you weren't around."
He then said, "where was I?"
I said, "you weren't born yet."
He then said, "but where was I? Was I in the ground? Isn't that where people are when they aren't alive? or was I in mommy's tummy?"
I said, "you were just a thought in my mind."
He didn't like this answer and said, "ok but where was I? I had to be somewhere."
He was very persistent and wanted an answer and I didn't have a very good one to give.