Imagine your surprise when it turns out not to be up to you!
That sounds flippant, perhaps, but behold: I knew lots of kids growing up whose (usually extreme Southern Baptist) parents tried to prevent them getting hold of porn, but I didn't know even a single one whose parents succeeded at so doing; those who couldn't get it themselves, and who didn't have friends willing to share, at the very least had acquaintances willing to be paid or otherwise persuaded to serve as brokers.
This held true even during the year I spent in a Mississippi reform school which operated as an arm of a Roman Catholic monastery, and where getting caught with such outrageous contraband bought you a half-dozen wallops on the bare ass with a razor strap from a monk who was serious about it, the sort of thing that'd leave you sitting lightly for the better part of a week.
I'm not sure whether anyone actually believed this had any dissuasive effect on the older students' desire to possess pornography, but anyone who did so believe was destined to be disappointed; indeed, the only effect such punishments had was as a strong incentive to develop the skills of misdirection, concealment, and lying with a straight face. (Me, I'm a cynic, and I half suspect that that was the whole point. If so, whoever designed the curriculum deserves some sort of award for unparalleled effectiveness in pedagogy.)
The point is, even in an environment which was by design totally inimical to it, everyone who wanted it had as much porn as he could keep hidden. (Which, in a couple of memorable cases, was a three-ring binder full.) In a more permissive environment, where hiding one's stash was a simple matter of keeping it out of sight -- rather than, say, getting hold of a contraband razor blade and waiting until after lights-out to carefully slit a mattress seam where it didn't show -- the question didn't even arise, even for those of us not so fortunate as to have what was then the rare prize of unmonitored access to the Internet. Now? You'd have to not only homeschool your kids, but keep them locked up in the basement all the rest of the time, and even then I wouldn't lay odds against their finding some way to get hold of porn -- after all, in extremis, all it really takes is a hormonally overheated imagination and a pencil, and the pencil is optional.