We have tended to use the locking pins for our kids collections, but even these aren't without problems - remembering to have the allen key if they want to trade, and we have found some pins' pin has snapped off at the solder with the badge (if you see what I mean). Perhaps if you get the locking backs they could have a trading set and a keeping set, with the trading ones being the ones taken to the parks and attached to the lanyards with the locking pins and then the keeping set are left at the villa safe and sound. Obviously pins could be swapped between collections as fashion/favouritism dictates!