Today is the feast of the Holy Innocents  or Lá Crosta na Bliana or the cross day of the year  in Irish.  The day was also known as La na Leanbh/  day of the children.  In Irish tradition this day was seen as a ill-omened or unlucky day  because it commemorated the  murder of children by King Herold.

Murder of the Innocents

In days gone by in Ireland this day was seen as an unlucky day,  so people would do all they could to refrain from  beginning any work or commence a new enterprise. If something urgent occurred that necessitated work, such as a burial , to avoid the bad luck the task was to be commenced before midnight of the 27th. According to Danaher if a grave were to be dug  on this day the sod must be turned  the previous evening (Danaher  1972, 258).

He also says that

In many places the ominous character of the day continued through the coming year. Thus, if 28th of December fell upon Monday all Mondays were unlucky, and similarly for all other days of the week (Danaher 1972, 258).

I had never come across this tradition when growing up and when I asked my parents neither remember this so perhaps it had died out in our locality at least 60-70 years ago. I would be very interested to know if any of you were familiar with this old superstition or keep to  it today.  For some non Irish traditions  for this day,  Spainish  and Mexican

References

Danaher, K. 1972. The Year in Ireland. Irish Calendar Customs. Mercier Press.

http://www.irishcultureandcustoms.com/ACalend/StStephens.html