You cannot "check" your kids phones, whatever you may believe, absolutely anything can be hidden by using apps or file managers. I have an app on mine, a photo and message "vault". It looks and works exactly like a regular calculator, until I type in a specific series of numbers, then the app opens. There are literally hundreds of these types of app on the Play Store. So, all those parents who "check" their DC phone are wasting their time.
And "burner" phones are sold for £50 around here, the kids even joke about them they are so common. So all that life 360 and parental software stuff is pointless too. Lots of kids swap "burner deets" and some give their "real" handsets to friends who will hang out where the child is supposed to be, in case their parents have a location app, but the DC is actually somewhere completely different and using their burner.
Kids will ALWAYS find a way around.
If mobiles didn't exist, no iphones, no apps, nothing, and I invented one, with all the current social media and browsers pre installed, they would never allow me to sell it, citing child safety concerns, privacy, stalking potential, access to porn etc.
We have sleepwalked into a mass surveillance society, where "social credit" is now as real as your Experian score. A single 30 second TicTok clip can ruin your business, get you fired, make you unemployable, drive you to suicide.
I'm not sure what the answer is.