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.
Their testicles get bigger and hang lower. Often one hangs lower than the other. Their penises grow larger. Their penises also get hard more often and unexpectedly. Boys usually start growing beards after their voices change.