17 Then was fulfilled that which was spoken by Jeremiah the prophet, saying,
18 "In Ramah was there a voice heard, lamentation and weeping and great mourning, Rachel weeping for her children and would not be comforted, because they are no more."
Matthew 2:16-18 (21st Century King James Version)
As the story goes, the Three Wise Men stopped by King Herod’s place asking for directions to the birthplace of Jesus, the King of the Jews. King Herod, himself being the King of Judea thus the King of the Jews, understood that this put his title into jeopardy. Not quite understanding the purpose of the the Three Wise Men’s visit he asked if they knew where Jesus was, so that he could worship him (you’ll remember from the previous sentence that they had stopped by to ask him that very same question) with the intentions of killing him. One thing leads to another, the Wise Men dream of Herod’s intentions and an angel visits Joseph and Mary giving them a head’s up and a chance to flee to Egypt. Herod, one step behind the rest, proceeded with his infanticide intentions, but unable to find the infant of choice decides to just randomly go after all of the male children two years old or under. This became the Massacre of the Innocents which allegedly took place on December 28, 0000. The result of the massacre varies from 6, according to the 1910 version of The Catholic Encyclopedia, to 64,000, by an early Syrian count.
Somewhere along the way the slaughter of innocent children became cause for pranks and the tossing of water balloons and eggs on unsuspecting passers-by. The belief, to the best of my understanding, is that the slain children of Herod are often considered the first martyrs for Christ (an act which an all likelihood was underappreciated as Christ was just 3 days old and not in any condition to be receiving martyrs). So, as it stands when on December 28 a child hurls an egg in one’s direction, that child is considered innocent or without sin and is not to be scolded or reprimanded. Ultimately it has become a watered down version of April Fool's Day.
(I should clarify my use of "watered-down" to mean that it isn't as highly recognized as April Fool's Day. In fact the only celebration of it that I have seen is more in the pueblos and less in the cities).
