In a PA28 I got my 9 yr old godson to sit in the back, much to his dismay. I didn't fancy having such a young person in charge of the only exit route. He still loved the flight though, his mum sat in the back with him throughout which would have been handy for any turbulence issues - of which there were none.
After 20 mins or so I started to hear static and clicks in my headset, I fiddled with the radio, tried to understand what was happening, asked for silence from the passengers etc. until his mum noticed that he had got a little bored and was pulling the headset plugs out, then back in, then out, then back in.. Doh!
At the end of it though he claimed it was the "best day of his whole life ever!". Brilliant.