"Mommy, when I grow up will I have the same head?"
Yes, Sweetie, your head isn't like your baby teeth. It's not like you have a baby head that falls off so your grown-up head has room to grow.
"Baby head? Baby head? Ha ha ha ha ha!"
"But, will you still be my Mommy and Daddy when I grow up?"
Yes, baby, we will ALWAYS be your Mommy and Daddy for ever and ever.
"Mommy, I wish I was eight already so I would be bigger than you."
Oh, I don't wish that. That would make me sad.
Because then I wouldn't get to see you when you are five and six and seven. Besides, I might not recognize if you were suddenly eight.
"Well, I would just put a hook on you and the hook would recognize me and say, 'THIS-IS-E.' - like a robot."