Whiz....what's a whiz like cheese whiz??

I'm not entirely sure what the protocol is for explaining the difference between a baby boy and baby girl to a 6 year old but non the less she schooled myself and my mom... "Mom you know how you know if your having a boy or a girl" "uh tell me please" "ok well the dr takes a picture and checks to see if the baby has a short one or a long one" "um what??" "You know a whiz, if its a long whiz it's a boy" "a whiz??" " yea mom a whiz! Don't you know these things yet?" uhhh apparently not, I should prolly head back to sex Ed 101 I have a lot to learn.