branded,
I've had the same thing happen. In my case it was a 10 year old that dad wanted to learn to fly. I was out with him on the buddy box, when we landed I turned around and dad was gone. The kid told me that his dad had errands to run and he was supposed to stay with me until dad comes back. It's sad that all of the rules that I have about being an instructor come from actions of jerks like that. I now have a rule that if the kid wants to learn to fly I tell them that I will teach the father and he can teach his own son. I'm not a baby-sitter. (note: I have made one exception since I made that rule, and that was for a kid who's dad was stationed in Iraq. Now that dad is back both father and son are regular flyers at our field)

That's my 02¢ worth