It doesn't really have a name as such but was more a bizarre phenomenon which occurred several summers at School. We had a large field with a small woods that we were allowed to play football and amuse ourselves with every break time. Now break could last for over two hours as we had a benign and much loved headmaster who would allow morning break to carry into lunch time (this was a payback from having to sit inside and sing along to his piano when it rained). Since we had so much free time imaginations were given full reign. Kids would start to collect acorns, twigs, stones and pretend to run shops and trade with each other. If this was not strange enough someone even created a primitive fruit machine out of a funnily shaped half of a tree trunk base. These shops became jealous of each other and would occasionally attempt raids for disputed pieces of woodland booty. My involvement was that as a boy we would often be asked if would guard against raiders, spy, or even carry out raids ourselves. The politics that became involved were scary considering we all between five and eleven. That, and none of the merchandise had any real value, or was even desirable.