Invasion of privacy can be a good teaching moment.

Don't wait until they've embarrassed themselves: take them through their browser history before they've even thought about porn. Show them router logs before they include pornhub entries. Show them their tracking history while they were far away from you, out with grandma. Explain that you don't look at these things, but that this sort of information is available. That if they use their school's wifi it's available to their teachers. If they use their friend's wifi, it's available to their friend's dad.

Do it while the information isn't embarrassing, and they will learn to protect themselves, rather than be upset about your "invasion".