If it was me, I wouldn’t have any concern over trading them. First, other characters have copyright and trademark protections, such as those as from Star Wars, and basically every other Disney-owned character (I think but am not positive that Mickey himself recently became part of the public domain). Generally, theses pins are traded ‘all the time’.
Second, the pin trading is advertised / promoted by the park, Disney; the copyright owner.
Third, it’s not a sale (e.g., churning out thousands of Marvel hoodies and selling them at a craft show or Etsy or something along those lines) of the copyrighted work.
Fourth, even if it did violate the copyright, which I don’t think it does, it’s so incredibly small-scale for a person to trade a handful of pins, that I don’t think they would ever try to enforce the copyright. Even if they did, what would the damages be: I gave you 2 Disney copyrighted pins in return for you giving me 2 different Disney copyrighted pins?!
Fifth, they would need to actually be able to identify the copyright breaker, (eyes on every pin transaction in the park?!!?!) and even if that transaction was flagged, I’m guessing with copyright protection in general (say, me selling those thousands of Marvel hoodies) there is a duty or at least expected custom for a good-faith warning to stop, before attempting to protect the copyright in civil litigation. If on the very off-chance told to not trade the pin, well, don’t trade the pin. I don’t see civil litigation resulting in the trading of it even if warned 100 times, for the above reasons and the cost associated with protecting the IP.
If it was me, I’d trade away.