Ahhh here's the thing though, in such a case you don't really need their location right that second. There's nothing you can do. They will be taken to a hospital and will be taken care of. Of course you would love to be there for you children the second they are in pain, just like when they fell on their face when they just started walking, but you don't need to. As a parent you have to accept that from when your kids get into their teenage years they will start to become independent, they will have experiences (good or bad) without you and they will be just fine. Or they won't be fine. But you certainly couldn't have prevented them getting run over, getting robbed, abducted or raped by having constant access to their location.
>you start worrying about things you never worried about before.
And you always will worry, trust me. Even when your kids turn 30, you still worry. You have to try to look at this objectively instead of with your feelings, people start being independent and there's nothing you can do about it. You will have to learn to let them go. What's next, do you want body function trackers installed so you can check their heart rate to see if they're still alive or their glucose level to see if they have already had their lunch yet?
