yes i agree it should be available... at 13 they may be 'technically' and legally children, but lets face it physically and mentally they are not ...
they are young adults - they usually have breasts and curves etc, most have started menstruating and they have sexual feelings and emotions and are old enough to act on them, and so do the young boys who are chasing them...so simply telling them not to do it, is naive, confusing and quite simply does not work - it has been the approach for decades and if it worked we wouldnt be having this discussion.
i dont believe being on the pill will encourage underage sex - if they want to do it they will - the fear of STDs and pregnancy is not usually the main reason a girl says no ...
they simply invent other ways they believe will work - i have heard of crisp packets, sandwich bags, downing vodka, jumping up and down, douching,etc etc so why not just give them an eductaed, safe and correct way to deal with it?