December 28 is the Feast of the Massacre of the Innocents. In the nativity story, as part of King Herod’s search of Jesus, he orders his army to capture any male children under the age of 2 in Jerusalem (or Bethlehem) and have them killed, as he had been led to believe that this child would end up deposing him as king. These children who were murdered are the Holy Innocents, another group of early martyrs, although they weren’t faithful, but being so young, and having died because of someone seeking our Jesus, they were made into saints and various miracles have been attributed to them.
During the 12 days of Christmas, in many Spanish speaking countries, this day is their version of April fools day, with people playing pranks and tricks on others, and sometimes the prankster or the prank is called an “inocenta” as a reference to the innocents and that because of this day, it is acceptable to engage in such childish behavior.
There are also some interesting medieval traditions associated with the observance of this day. In some parts of Europe, this was a day of misrule, with adults dressing their children in adult and tradesmen clothing, and allowing them to run and demand things on that day. This would extend to a child wearing the bishops vestments in some places, and giving dictates for the day.

Another medieval tradition was that whatever day of the week Holy Innocents day fell on, this day would become a de facto vacation day in some areas, as it was considered unlucky to start or complete any work on that day of the week until the next Holy Innocents day in December which would change which day of the week.

There is a tradition within Catholicism which talks about the octave of the major feasts, primarily Christmas and Easter. Essentially the 8 days following the feast are considered to be an extension of the feast, until 8 days later which would be the same day of the week the feast was on. As Christmas moves around more, and 8 days later is New Years Day, this make New Years very holy, and that feast is considered in some ways to be as holy as the Feast of the Nativity. It also indicates that the day of the feast makes it consistently holy for the rest of the year, which I found explicitly stated for the Holy Innocents, but implied through the recognition of the Octave of Christmas. This is purely my speculation, but one could see that day of the week that Christmas falls on particular blessed for the next year, only shifting until next Christmas.

As this Christmas was on a Sunday, it signifies that Sunday is particularly blessed for this year, which is doubly enforced by Easter Sunday.