This concerns me a bit. I'm all for public safety, but as mentioned in the article, the potential for misuse/abuse is absolutely a huge issue.
Allowing a system to track you when you've initiated a 111 call I'm on board with. But having the ability to arbitrarily track someone under the guise of safety, I think is a stretch. Having "Rules" in place will not stop abuse. Having technical barriers is more likely a way to prevent abuse (the only way is by not developing it full stop).
If the system is to be used for people like dementia patients, I think it really should have a POA or themselves if they are cognizant enough, have to sign them up to the service to have their device tracked, similar with kids. A Parent should need to sign up their kids device.
It will of course need some kind of administration and integrity built in, to ensure someone can't just go and "add a number".