CDMA Firefly In The Works

I seriously thought about getting a GSM one of these from Target for my 6 year old. From what I could tell I could stick in a family plan SIM card and have her linked up for $7 a month on T-Mobile (apparently the Firefly isn't SIM locked). But I decided to give it a miss because actually what I really want is a way to find out the location of the phone. Not just so that I could find my kid (I'd clip it to her belt) but also so I could find the phone itself if she lost it. That would definitely happen to her at least once.
I'd be willing to pay a $1 extra a month to have that feature - okay carriers - GO!