ah, it always helps when you give concrete examples of what you actually mean
your OP was worded so it might have been about pretty well anything from sex education in schools to trafficking of youngsters
well, if it is about porn then I think there is quite a lot you can do:
make it clear that you will not have this kind of reading material in the house because it is degrading to human dignity/women/etc- this will not stop them from ever seeing porn but it will make it very much harder for them to develop or feed an addiction
keep an eye on computer use
don't assume that any interest in sexual matters is connected with any other interest in sexual matters and that you have to clamp down on it all- in fact, a 16yo who has a healthy relationship with a nice girl is probably far less likely to develop an unhealthy interest in hardcore porn
cultivate an open and positive attitude towards sex as a means of human interaction rather than a commercial commodity or a means of dominating other people
make sure any adult males in the house are a good role model in the way they speak of women and behave around women
maintain high standards in how you speak about people
help them to develop other interests