Their breasts begin to get fuller. Often one breast grows faster than the other. Their hips get rounder. Their waists get narrower. Their vulvas and clitorises grow slightly, too.
Many girls have a white, sticky discharge from their vaginas.
This is a perfectly normal sign that the changes of puberty have begun. Sometimes, this discharge gets on a girl's underwear. She shouldn't worry about it unless her vulva becomes itchy or irritated. If it does, she should visit her doctor or clinician. Boys see hormonal changes, too.