In the future they will use shady FinFisher iTunes and other exploits to grab the data then seize the phone.
https://9to5mac.files.wordpress.com/2013/07/screen-shot-2013...
Note the "slide to unlock" message at the bottom. If you asked most users what it means to unlock a phone, this is what they would think of, as they see it every day.
[citation needed]
"Unlocked phone" is not limited to experts. More than half a million hits on google: https://www.google.com/search?q=%22unlocked+phone%22&oq=%22u...
I really don't know what "most users" would think of.
Edit: I understand your point and agree that unlocking a device would not mean exactly the same thing to all people. I just don't agree that the parent needed an additional citation.