How do they do that?

First, she's on your hip every day, you're having rocking-chair, bottle, baby schmooze time every evening, and she's scribbling and learning letters with you. Then you blink, and she's showing off her jumping skills, having real conversations with you in near-perfect grammar, and drawing people and "reading" along with you at storytime. Lately it seems like every day brings up something new that makes us say "Hey- when did you become a girl? Not a baby, but a girl?"