How did the "Marco Polo" game, where one child says "Marco" and another responds with "Polo", come about?

The game is fairly new having begun right after WWII. There was a bridge called "Marco Polo" right outside of Wanping (by Beijing)China. The League of Nations had given the the West side of the Bridge to China and the East to Japan right after WWI. Although there was a treaty that said Japan must tell China of any military action in the area, Japan failed to notify China.
On July 7, 1937, at about 23:00 (that's 11 pm to me) Japan had a training military excerize on their side of Marco Polo Bridge. China's soldier, thinking they were under attack, fired back with little consequence.
The initital event lasted for only minutes. Both sides rushed to their leaders with news of attack. Japan was missing a man and believed he was lost in the river below (really a rice field). War was declared and it lasted July 7-9th, 1939.