I'm not a parent and a bit autistic so excuse the unemotional reply but surely there are other ways not to have anxiety about your children surely?:

Teach independence/self-defence/street smarts, encourage weight lifting for older kids, therapy/meditation for yourself (some anxiety is natural of course!), move to a safer city, have more children (easier to pair them up on adventures, plus less subconscious physiological fear of losing your one and only child), distract yourself and stay busy, go with them to places the first few times to assure yourself then take off your training wheels. Or just say no to certain things.

It doesn't seem to me a special case of anxiety that can only be addressed by spy apps and knowing you might be able to instantly contact them.

lol, have my kids carry a phone or have more kids so the can be paired up.

That’s a wild thing to say out loud. And absolutely doesn’t solve the problem. Kids need to have their own friends and own social circles if you want to teach independence.

Knowing where they are isn’t necessarily “installing spy apps,” it can just mean being able to call them or text them.

“Move to a safer city” is a lot more expensive than a phone plan. A lot of people don’t have that luxury.

I agree that all the things you talk about are life positives but the way I see it, giving a kid who is old and mature enough to use one a cell phone is like a $15/month cost proposition for an outsized benefit of being able to contact them.