Listening to an I-pod sends a message to other people. That message is this:

"I'm ignoring you. You aren't important. What's being piped into my ears is more important than anything you might have to say."

There's nothing wrong with sending that message under appropriate circumstances (like on a train commute home after a long day), but it's not a good message to send a kid you're supposed to be having some "quality time" with.