In the opening scene, the cop is played (in an uncredited role) by Randolph Mantooth, best known for playing paramedic John Gage on "Emergency!"
More likely this episode was titled May Day in recognition of the Haymarket Massacre of 1886 in Chicago and as a nod to a traditional spring celebration often featuring children.
The title refers to the first day of the month of May, a holiday celebrated around the world for different reasons. The U.S.S.R. celebrated it as a Communist holiday known as Loyalty Day starting in 1958. The U.S.A. celebrated Law Day on the first, while many countries in the world celebrate International Workers' Day, or Labour Day.