DS5 took to pin trading like a duck takes to water. Pins can be obtained in the park. Many people buy pins online or at Disney outlet stores to save money. These pins can be traded with other guests, but mostly with cast members.
Most cast members throughout the park wear lanyards with pins. They have pins you want. If you have a pin they don't have, they will trade you. Some cast members wear a green colored lanyard which is exclusively for trading with kids(12 and under, I believe). Its a another great way to get kids to interact with people(break down the possible barriers for later character interaction ?).
So get yourself some pins and get to it. Lots of fun to be had.