My phone and computer have passwords only I know.
But we lock all other electronics (ipad, game controllers, TV remotes, James’ computer) in a locking file cabinet.
Devices are only unlocked after all homework and chores are done.
All devices re-locked up before bedtime.
For bluetooth device tracking (i.e. finding lost, or hidden-by-your-child devices) you might consider super-glueing a “tile” or “tile slim” to them.
www.thetileapp.com
(BTW I have a tile on my keychain, and it has saved me countless times.)