The worst thing was even my 8 year old daughter could tell that it was a helicopter by eye, so they were close enough. Red Arrows commentator mentioned that the heli called Luton for a traffic service and Luton then informed Old Warden/Red Arrows. How hard is it to read a Notam?
Edit - to say that it was still a great display and both kids are still talking about it. My son thinks it's great to talk like the red arrow commands "Foooood.... GO! Pyjama... GO!" and is trying to grab my headset now... if only I could fly like them