There is a huge attack surface for this. For example, kid manages to buy an old phone. Resets the phone and creates an account. Kid buys something like a Pi 3 manages to get a regular phone to become an access point. Etc. If a laptop is not completely locked down, a kid might boot a live USB stick.
replyBarriers like that for accessing 18+ sites would be so much better than nothing.
replyAnd cheat devices can be taken away as soon as the parent notices them.