My DD 6 loves pin trading. It's a great way to spend time when you're tired of waiting in lines. And it actually has cut down on the number or worthless souvenirs that we buy. She spends so much time looking for CM's with lanyards and she loves the pins so much that she hardly ever asks us to buy anything else. She always gets a great thrill when she spots a CM with a lanyard and she often ends up having great conversations with the CM's as she looks at their pins.
At the beginning of each trip, we start by finding the cheapest pins we can and buy a few characters that she does not like. Otherwise she wants to just keep the ones we bought instead of trading them. At first, she would just trade for any pin that she liked. And once she had traded all of the "bad" ones that we bought, it was hard to get her to trade up to "better" pins. Now though, Ariel is her favorite character and she will only trade for an Ariel pin. Ariel is hard to find so she usually only gets one or two per trip. But she gets a huge feeling of accomplishment when she finds one. And she remembers trading for each one and loves to tell about how she got them.