My son got into pin trading this past summer. Yes, it is very popular at DL so they will have a blast. Be sure to visit with the 'professional' pin tradings that hang out right now around Plaza Pavillion. That is the temporary location while the Buzz Lightyear ride is being built. I'm not sure if they'll move it back or not, I haven't heard. Many of these folks love to talk to the kids, but you will find some that just want to talk to other 'professionals'.
One thing I did notice at WDW this December was that there were more CMs trading than at DL. The drawback of that was that many of the CMs didn't know the 'rules'. I had to stop my son many times from trading for non-Disney pins, Sedesma pins or even plastic pins. We've never had that problem at DL.