You're upset that your daughter was lost, and everybody understands that. But you must consider what it means to have what you ask for become a trend, and to have the infrastructure built to make it easy to do.
Perhaps when your child is 6 nobody will claim she has any rights, and you are free to lojack her. But then we will have to ask the question, when does she gain some dignity and rights, at what age does it become a bad idea for you to do this? At what age should it actually be illegal for you to do this? We have not had to ask that question until you do it.
Location services all beg the question of what to do when one person is in power over another and can demand location data. You can over your young child, and more debatably over your older child. Can employers ask it of employees? On their breaks? Can husbands ask it of wives? Not demand it, you understand, but ask, as in, "Honey, what's wrong with me knowing where you are? Think how handy it would be. Don't you trust me? Don't you love me?"
This is the world you will help build. But it gets worse. You see, there will be flaws in the system. Not just hackable security issues, but mistakes. After a custody battle, somebody will forget to turn off the non-custodial parent's access to the location data on the child. This will assist in many kidnappings. (As you may not know, the vast, vast, vast majority of kidnappings are by relatives. The random stranger that everybody is afraid of barely exists.) Perhaps not in your case, but in many people's in this world you are creating.
A better idea? Teach your child, if lost, to approach a suitable adult, and hand them a card or show them her bracelet, which has your cell phone numbers on it. We tell children not to talk to strangers, but we forget to mention that means not to talk to strangers who approach *you*. It is perfectly fine to talk to strangers the child selects for help, more than fine, it's the right thing for her to do. Or sew the number in the lining of her coat, or shoes, or lunchbox or whatever. If you really think it's bad for her to approach strangers, teach her to identify police, teachers, people in uniform etc, but tell her that if she can't find one of those to approach any nicely dressed person.
She'll be fine.