Parents already have the ability to lock down Android or iOS devices for their own children, if they choose to do so.
Super awesome as long as your kids never go anywhere they could access a non-locked-down device. And assuming that device parental controls work, which (at least on iOS) they don't [1]. 1. https://www.macworld.com/article/2305919/apple-parental-cont...
Please describe how requiring a government ID in order to use a computer prevents an over-seventeen from presenting their ID to unlock their computer and then handing that computer over to an under-eighteen? An over-seventeen handing over control of their unlocked computer to a visiting under-eighteen seems to me to be an under-eighteen "go[ing somewhere] they could access a non-locked-down device".
The only way I can see to even begin to combat that is to constantly surveil the operator of the computer to attempt to detect when its operator changes. Do you have a superior method?