Kathy Stinson's book "Big or Little?" perfectly describes how Elizabeth feels about life these days.
We can usually tell whether she's feeling big or little based on whether she chooses to sit in the big chair or the booster seat.
Sometimes we tell her she isn't allowed to do certain highly coveted things until she's bigger, like ride in Erika's car seat. Inevitably she'll sigh, stand on her tiptoes and reach way up high. "I'm pretty big NOW Mom!"
I'm usually Mommy or Mamma these days, but when she's exasperated with me I'm always Mom, with a very long o.