This is a subject I brought up with some friends not too long ago. The earliest memories I have are of when I was probably around 5. One that I know I will never forget from that time is when I was at the babysitter and I was hitting some t-ball when I sister walked behind me. Well, she ended up having a bump about the size of the ball on her forehead. I wouldn't count on her remembering anything before that day. I'll have to ask her if she remembers that as good as I do.