My reactions on hearing at least one version of the tape.
The kid obviously enjoyed it.
The pilots on the tape definitely enjoyed it.
By no stretch of my imagination can I see how safety or 'security' was compromised. My visual has an adult whispering in the kids ear and standing by with finger on a spare mike button if needed.
Kid was easier to understand than some of the 'real' controllers I've had to work with here and there.
My opinion - total non-issue. If the FAA were the exact opposite of my opinion of the way they actually are, they would suppress a smile and tell him "don't do it again without permission'.
Then they could go focus on stuff like kids who commute from California to fly from Newark in the winter with a pilot who flunked numerous check rides and spent the entire flight blabbing to her about everything except how to recover from a stall.