Parents and caretakers have the ability to restrict children’s content on any device a child has access to. The burden should be on them to ensure their child is not consuming porn. It shouldn’t be everyone else’s problem that people are unwilling to parent their children.
Minor children really shouldn't have an expectation of privacy while they're out on the big, bad Internet. The best advice is for families to have computers in common areas only, where children's screens can be noticed and observed by parents at all times. That's not so much about a lack of trust in your own children, but beware the rest of the Internet.
By all means, teens can be granted increasing privileges and privacy as they grow up and begin to have their own lives. IF you as a parent have fostered their trust and you've inculcated "street smarts", then at a certain point you let go and trust them as well. Amazing how that all works.