The Holy Innocents are the children mentioned in St. Matthew 2:16-18:

“Herod perceiving that he was deluded by the wise men, was exceeding angry; and sending killed all the men children that were in Bethlehem, and in all the borders thereof, from two years old and under, according to the time which he had diligently inquired of the wise men. Then was fulfilled that which was spoken by Jeremias the prophet, saying: A voice in Rama was heard, lamentation and great mourning; Rachel bewailing her children, and would not be comforted, because they are not.”

It is impossible to determine the day or the year of the death of the Holy Innocents. All we know is that the infants were slaughtered within two years following the apparition of the star to the Wise Men. The Church venerates these children as martyrs; they are the first buds of the Church killed by the frost of persecution; they died not only for Christ, but in his stead. In connection with them the Apostle recalls the words of the Prophet Jeremias speaking of the lamentation of Rachel. At Rama is the tomb of Rachel, representative of the ancestresses of Israel. There the remnants of the nation were gathered to be led into captivity. As Rachel, after the fall of Jerusalem, from her tomb wept for the sons of Ephraim, so she now weeps again for the male children of Bethlehem.

The Latin Church instituted the feast of the Holy Innocents at a date not before the end of the fourth and not later than the end of the fifth century. It is, with the feasts of St. Stephen and St. John, first found in the Leonine Sacramentary, dating from about 485. The Latins keep it on 28 December, the Greeks on 29 December, the Syrians and Chaldeans on 27 December. These dates have nothing to do with the chronological order of the event; the feast is kept within the octave of Christmas because the Holy Innocents gave their life for the new-born Saviour.

In England the feast was called "Childermas".

The Roman Station of 28 December is at St. Paul's Outside the Walls, because the church is believed to possess the bodies of several of the Holy Innocents. A portion of these relics was transferred by Pope Sixtus V to Santa Maria Maggiore. The church of St. Justina at Padua, the cathedrals of Lisbon and Milan, and other churches also preserve bodies which they claim to be those of some of the Holy Innocents. In many churches in England, Germany, and France on the feast of St. Nicholas a boy-bishop was elected, who officiated on the feast of St. Nicholas and of the Holy Innocents. He wore a mitre and other pontifical insignia, sang the collect, preached, and gave the blessing. He sat in the bishop's chair whilst the choirboys sang in the stalls of the canons. They directed the choir on these two days and had their solemn procession.

Other Saints of the Day
1. Saint Anthony the Hermit
2. Saint Caesarius
3. Saint Domnio
4. Saint Romulus and Conindrus
5. Saint Troadius