Any "child" who is old enough to be out "late at night" should be responsible enough that he doesn't have to be connected to Mom by a walkie-talkie.
I can think of an example of that.
We were at a fair (local, small one) last week.
My daughter met a friend there and she and her friend went off to do some big kids rides. The other mom and I put their cell phones on them and some money with their ride bracelets and let them go.
We pretty much followed their paths the whole time...but there were many moments we couldn’t see them.