As a pilot (albeit not on big-jets), when I fly and talk with ATC, I want to be sure that the guy or gal on the other end of the RT is competent. Whilst the pilot ALWAYS has the ultimate rsponsibility for safety, if I'm meant to be following ATC instructions I want to know that they are considered istructions issued by someone appropriately trained, qualified, licenced and in current practice.
Next time you fly, think about a child giving instructions to the aeroplane you're sat in. Think about what'd happen if, despite being told what to say, the child said the wrong thing, and then before it was corrected there was an r/t failure - such chains of individually inconsequential failures, linked together, can easily end up in disasters. If you ever listen to ATC, think about listening to pilots in training who, having been told what to say by their instructor, still hesitant and mix things up. Can a child really do it properly. And consider the spurious ATC transmissions from unauthorised sources that have happened in the past - how does a pilot tell that this child is genuinely passing on instructions from a real controller?
This is potentially lives at stake, and millions of dollars worth of equipment in the firing line. It absolutely horrifies me that anyone would allow such a thing to happen. Why is it any different to the Aeroflot A310 incident some years ago when the pilot allowed his child into the pilot seat when the airplane was in the cruise? (that resulted in a crash, for which the pilots were very rightly blamed) What was that guy thinking putting a kid on the mike? I don't care if the kid was "supervised". Anyone in ATC who did that, I would very seriously question their judgement and competence to be an air traffic controller, and I'd certainly have a significantly reduced confidence in the reliability of any instructions that the guy gave to me himself, let alone those from the child.
IMHO the guy(s) who allowed this to happen should be fired, and potentially brought up on a charge of willfully endangering aeroplanes too.
Andy