As every parent, legal guardian, older sibling, etc should. That's their job in making sure that when the time comes, their offspring [or anyone that they take care of] should know about where babies come from, how to protect themselves from STD's and unwanted pregnancies, etc.
I've ALWAYS hated when a parent doesn't do this part of the job (speaking from experience in regards to my Dad & stepmom; glad that they at least learn their lesson when the time came when their kids became of age). Met a few over the years, fricking pisses me off.