TCF, with all due respect, just because it is worse somewhere else in the world doesn't make us feel any better! You have detailed the south Fla situation on here before, and it sounds really bad. Up here in the Mid-Atlantic, cheating is not rampant at the 10U and 12U level. It exists, but it doesn't seem pervasive or systematic like it sounds like it is in your neck of the woods.
And to be clear, I don't think the other kid was cheating. He seemed to really think the ball was in. (I love how kids standing at the other baseline think they can see on the opposite baseline whether a ball is in or not...) The girl that was standing there wasn't really deterring hooking that much because no one was really sure what she was doing there. She was paying little attention and seemed to not fully understand the game of tennis.
No, sorry, I see now that junior court monitors, at least ones that young and without enough training, are a bad idea. Those crazy intimidating players you often rail about would've eaten this girl alive, and so it would be like a two-on-one match. A court monitor has the power to completely determine a match's outcome, and this is not an acceptable position to put a scared, nonassertive 11 or 12 y.o. kid in.