Kim,
You can click
here to read one of my prior Q&As where I provided more details about pin trading. You can also find some good overview information
here,
and much more detail at the
Disney Official Pin
Trading site (see the "Getting Started" section for lots of FAQ
answers).
Regarding the need to be careful, I would say that we have never had any issues trading. The one thing to keep an eye out for is to make sure that the pin
you are trading and the one
you are receiving have a
Disney trademark on the back. If you keep the trading limited to your kids trading with the Cast Members, I think you will not have any issues with this.
In my experience the much bigger issue is that the pins have a tendency to fall off of lanyards, especially if the kids wear them as they are running. To minimize this risk, you might either want to keep the lanyards yourself until the kids want to trade, or consider buying some of the heavy-duty pin back locks that they sell in many of the WDW stores and pin trading carts.
Enjoy your "full force" trading!!