What happened?

I was at breakfast the other day when a woman and her two teen aged children entered.  The kids were older teens, maybe 16 & 17, a boy and a girl.  The boy was wearing a tee shirt and shorts.  The girl had a tight shirt with quite a lot of cleavage showing and long pants.  When did teen aged girls get cleavage?  Where was I?  When I grew up we knew theoretically that girls grew into women and women had breasts but to actually show their cleavage?  No way.  Maybe Saturday night after a party you might get a private viewing but....  What happened?