5c Find My iPhone Not Working on Kids Phone

I purchased two iphone 5c's, one for each of my children. All of them have been parental locked, with application installation and safari blocked. Find my iphone has been turned on, then locked on with parental controls. Data is limited to 500 mb per month by verizon.

My son's device works perfectly when I use the "find my iphone" application on icloud.com.

However, my enterprising 15 year old daughter's phone only seems to show up in "Find My iphone" when she is at the house, and even then it is spotty. For example, today I logged in (8:20 cst) to find her phone, it has a grey circle that says "last location yesterday at 5:18". Most of the time when I check, it says "phone unavailable"....yet I will text her, and she'll text me back.

She called me this morning, and while I was on the phone with her, I logged into iCloud...same deal, it couldn't find a current position. So, I know at least that the mobile network was turned on.

I won't get into the reasons to need to track her phone, but I'll just summarize by saying that it's not to just be an overbearing parent. She has impulse control issues which have placed her life in danger several times.

She is doing something that is shutting the tracking down. Any ideas?

Would changing date/time do anything?

What about turning off wifi?

What about turning off mobile data?

Could she have installed an app to block find my iphone? (this only could have occurred on one of the few occasions when I had allowed installation of programs.)

She is extremely bright, and has found something or been told something by a friend.

Please help!