Obviously carrying a tracker doesn't keep you safe. What it does mean is that if someone is in danger eg if they are supposed to be walking to school and are suddenly travelling at speed (ie in a car) in a different direction, then loved ones can be aware that something is wrong, and make attempts to contact the person or intervene to prevent something worse happening, rather than not knowing there is a potential problem until after your child has been raped/murdered/assaulted.
But if someone is going to attack/rape/murder your child, they're going to switch the phone off and dump it at the first opportunity - so why would a tracker help?
It's not like I sit there staring it whenever my children are out of my sight. But in the event of them not being where they are expected to be at a particular time then I will have a look to see where they are. This can provide reassurance eg they are still walking from the station to school or raise a question - they are heading towards the park instead - which would lead me to check up on them that they are okay.
And what if they'd decided to switch their phone off or disable tracking?
It pings to tell me they have arrived at school. Since parents are legally responsible for their children's school attendance I think that knowing they are at school when they should be is indeed called good parenting, and just assuming they are there when actually you have no idea where they are would be called 'piss poor parenting.'
And again, what if they turn it off? Or turn up at school and then walk out again later with their phones off/tracking disabled?
Tracking only tracks the device, not the person. So if you rely on tracking to know where your child is, what are you going to do when it fails or they turn it off?
You could check and see your child is at Joe's house, and think they are, but in reality they could have gone out and purposefully left their phone behind, putting them in even more danger as they're now out with no way of contacting you for help.