If there’s a reliable way to only be alerted to specific activity, then the parents aren’t really actively spying, in the sense that the kids still have privacy when they aren’t transgressing into prohibited space. As long as that prohibited space is reasonable (huge debate possible there of course) and the kids know about the restrictions. imo
Is this a Deviant Art ad?
If you’re talking about masterbating, then that’s not unusual or a bad thing necessarily. I didn’t encounter porn until late high school yet I would do that frequency as a younger kid. That’s normal for boys. What’s not normal is that you seem to have pathologized it.