As a parent, part of the verbal contract with my kid is that if he wants to have a cell phone, computer, internet etc. paid by mom and dad, we have the right to search it when we need to. And mostly we only search it to bust him for finding ways through the parental restrictions to play games at 1am when he's supposed to be sleeping or finding a way to "accidentally" buy skins on Fortnite. Basically he knows the rules and that we can search his phone when we suspect he's been breaking them. Otherwise he's not old enough or responsible enough to trust with that technology.

So you mean I don’t have to have the illegal key-logger on my kids computers?

If he’s not old enough or responsible enough to have technology, then why does he have it? If you can’t trust them with it, then they shouldn’t have it. You wouldn’t give the keys to a Ferrari to a 13 year old and say, “sure hope you don’t drive this.”