Back in the dial up days, my dad installed a switch in the phone socket in his room (which was wired before the phone socket in the computer room) so he could disable the internet at night. I used to sneak in while he was snoring and crawl around the bed to switch it back on.

Point being, there's only so much you can do to prevent kids from accessing things they shouldn't. The right way to parent is to try and direct your kids towards the right things, but also offer age-appropriate yet honest explanations for the things they do find. But it's a difficult balance, as kids get older they deserve more privacy, and it's difficult enough for an individual to stay ahead of the tech curve than to keep your whole family on top of it.