Familymap

Yes, unfortunately any other application requires access to the phones to add software.  

Android device manager will run in the background, un noticed, but it still needs to be initiated on each device.

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Here is the take of a mom, who pays for the cell service....

Each phone is not unlike a credit card.  If lost, the finder might run up unexpected charges (data) before the phone can be blocked.  And it's an expensive item that I won't replace for them if it gets lost.  

So - they are each required to put android device manager or find my iPhone on the phone.  It is added on the premise that it can find the phone if lost or stolen, but can be used to locate the phone and it's user.

My oldest has actually called me to locate his phone when he left it at his fathers house once.

I don't let my kids know I can use it to track them.  EVER.  Trade secret....

Why these and not family Map?   

Family Map costs extra

Family map lets the user know it is being used and tips them off

Its annoying for both reasons when free apps do the job