Questions about how this is going to be implemented and enforced from a technical and legal perspective are missing the point/benefit: this is about empowering parents and collectively changing behaviours.
"It's against the law so no you can't" isn't going to work with EVERY 14 year old. But it will work for many and hopefully that's enough.
I actually see this as potentially damaging to society. "It's against the law for you to use any website that lets you look at cat pictures and make any contact with anybody else" is so silly that kids are going to see right through that, and rightly not care about following it. So they're going to have less respect for the rule of law generally...
I'm very big on compentent laws, but also on just not having silly laws. It devalues the whole system...
(I would also wonder how many 14-year olds you know if you think this would work for many, but also I suppose that could be a cultural difference)
My last ADSL router/modem from Vodafone (UK telecoms/broadband company - unsure who the OEM was) was amazing in this respect. You could configure it to have all the lights off by default, and it had an infrared proximity sensor built into the top - wave your hand to activate the blinkenlights.
LEDs on most networking equipment are software-controlled. I can disable them on my OpenWrt devices and even the Devolo stock firmware also included a feature to disable LEDs.
I believe it would though. It's already happening higher up the supply chain where conveyor belts of produce are graded using computer vision (and other techniques, I'm sure).
This is about moving these techniques further down the chain. A robot picker arm with a few cameras attached that can tell whether something is rotten is well within our grasp. (Awful pun intended!)
A new pair of dark-coloured jeans is enough to mess up light coloured seats; it's probably not 'dirt' in the traditional sense. (I agree with you that the staff should be ensuring the showroom stock is spotless.)
I think it might have been something by William Gibson? I believe she had to cut through the seatbelt and then call a friend to step out in front of the car causing it to career off the bridge and into the water, at which point the locks would release. (The ethics calculation deemed it preferable that she escape rather than perish.)
"It's against the law so no you can't" isn't going to work with EVERY 14 year old. But it will work for many and hopefully that's enough.