Hello, Laura!
Wow! You have thought of everything, Grandma!
Introducing your grandkids to the fun of Pin Trading will be such a fantastic memory for all of you! I know that we enjoyed allowing our two children to pick out their own lanyards and starter pins as one of their first souvenirs once we got to Walt Disney World. I suggest that you head to Downtown Disney and let them look at their options there, since it will be so much more magical and memorable for them to pick out their own items right there where the magic happens. Be sure to get pics of them, too! What great memories captured for all of you!
There's a great overview of
Pin Trading on Walt Disney World's website, so be sure to read it with the grandkids prior to your departure. This will give them an idea of what to expect once you get there. There's also a very informative post from Disney Insider which lists dozens of topics about
Pin Trading in Disney Theme Parks. Perhaps you can select a few of these questions and print out the answers to use as a guide for your grandkids as they learn the tricks of this very popular trade in WDW! :-)
Send more questions as you think of them; I'd love to help!