Holy Innocent's Day was considered a very unlucky day. The day called for a rememberance of Herod's massacre of the innocents. When the Magi informed Herod of the birth of the King of the Jews, he feared that he would lose his throne, and he reacted by ordering the murder of all the male children in Bethlehem. The Holy Innocents, as the murdered children were known, are considered to have been the first Christian martyrs.
The variant name for the holiday is Childermas, or rather: Childrens' Mass -or- Festival Day.
It was believed that a person should not begin anything on Childermas. Nor should anyone engage in any activity that would need to be repeated throughout the year. This included activities such as putting on a new suit of clothes; cutting one's fingernails, and so forth.
Henry Bourne, in his Antiquitates Vulgares; Or, The Antiquities Of The Common People, published at New Castle in 1725, noted that:
Thus have the Monks in the dark and unlearned Ages of Popery copy'd after the Heathens, and dream'd themselves into the like Superstititions, esteeming one Day more successful than another; and so according to them, it is very unlucky to begin any Work upon Childermass Day; and what Day soever that falls on, whether on a Munday, Tuesday, or any other, nothing must be begun on that Day through the Year;
King Henry VIII issued a proclamation on 22 July 1540 which forbid processions of children on Childermas. It might therefore be assumed, that such processions had taken place on that day in years prior.
It would appear that there would be no enjoyment to this holiday. But that was not the case. The children, and specifically the youngest child in the family or group, determined the food, entertainment and so forth for the day.
Traditional foods served at Childermas are anything with a red color, recalling the blood of the martyrs.