The feast day for the Holy Innocents is December 28. This picture is "The Slaughter of the Children of Bethlehem" by Gustave Doré. These children are mentioned in 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."
For more information, see this article about the Holy Innocents from Catholic Encyclopedia (1907).
Carols and hymns on this site which specifically honor the Innocents include:
A Hymn for Martyrs Sweetly Sing (Hymnum canentes martyrum), The Venerable Bede, 673-735, Translated by Joan Mason Neale, 1818-1866
All Hail Ye Infant Martyr Flowers (John Mason Neale)
All Hail, Ye Little Martyr Flowers (Athelstan Riley)
As Wolves Attack Their Helpless Prey (John Chandler, a translation of Molles In Agnos Ceu Lupus)
Audit tyránnus ánxius - For Laudes matutinĉ on The Feast of the Holy Innocents (SS. Innocentium, Martyrum)
The Angel Said to Joseph Mild (Luke Waddinge)
Coventry Carol - Version 1
Coventry Carol - Version 2
Flowers Of Martyrdom, All Hail! (Edward Caswall)
Glory, To Thee, O Lord
Hail Ye Flowers of Martyrs
Hail, Flowrets of Christ's Martyr-Crown (William J. Copeland)
Hail, Flowerets of the Martyr-train ()
Hail, Infant Martyrs, New-born Victims, Hail! (John Chandler, a translation of Salvete, Flores Martyrum)
The Holy Innocents - Laurence Housman
The Holy Innocents To-day (George R. Woodward)
The Hymn For Conquering Martyrs Raise
Hymnum canéntes mártyrum - For the Officium lectionis on The Feast of the Holy Innocents (SS. Innocentium, Martyrum)
Jesus Christ Of Nazareth
Let Faithful Quires The Carol Raise
Little Flowers of Martyrdom
Mark This Song, For It Is True
Marke This Songe For It Is Trewe - Version 1
Marke this songe for it is trewe - Version 2
On This Day Earth Shall Ring - Version 1
On This Day Earth Shall Ring - Version 2
Sweet Flowerets of the Martyr Band - Version 1 (Sir Henry W. Baker)
Sweet Flow'rets Of The Martyr Band - Version 2 (Sir Henry W. Baker, alt.)
That Rage Whereof The Psalm Doth Say
Thee, Christ, We Laud And Magnify
Upon the Twenty-fifth of December (Roxburghe Ballads, ca. 1700)
Welcome Yule (from Hutchins, Carols Old and Carols New, 1920)
Welcome Yule - Rickert
When God Was Born Of Mary Free
When Herod In Jerusalem - Version 1 (Davies Gilbert, 1823)
When Herod In Jerusalem - Version 2 (William Sandys, 1833)
When It Reach'd The Tyrant's Ear
The Winter Sun Was Setting
With Al The Reverens That We May
With Boding Fears The Tyrant Hears
With Terror Doth The Tyrant Hear
Weep, Weep, For Earth's Bereaved Ones
Ye Flowers of Martyrdom, All Hail (R. Martin Pope, a translation of Salvete, Flores Martyrum, from Hymn For The Epiphany, 1905)
Christmastide Poems of Christina Rossetti
- Holy Innocents ("They scarcely waked before they slept" & "Unspotted lambs to follow the one Lamb"), p. 159
- Holy Innocents (Sleep, little baby, sleep"), p. 309
Christmas Poetry of Catherine Winkworth
- The Christlike Heart ("Dear Soul, couldst thou become a child")
Finally, although most refer only to the Magi, some of the songs relating to Herod also relate to the slaughter of the Holy Innocents, including
All Hail, Ye Little Martyr Flowers
An Infant Lay Within A Shed
Augustus Caesar Having Brought
Be Still, My Blessed Babe
Be Still, My Blessed Babe - Husk
Carnal and the Crane
The Black Decree
The First Day Of Yule
From Church To Church
In The Reign Of Great Caesar
Mary Had A Baby
There Joseph On His Sleeping Lay
The Three Kings - Version 3
Three Kings' Song
Unto Us Is Born A Son - Version 1
Unto Us Is Born A Son - Version 2
When Herod In Jerusalem
Who Are These Who Ride By Starlight
Carl P. E. Springer writes that a hymn for the Feast of the Holy Innocents has also been derived from the poem, Paean Alphabeticus de Christo. The De Innocentibus rubric begins with the 10th verse:
Katerva matrum personat
Collisa deflens pignora,
Quorum tyrannus milia
Christo sacravit victimam.
The remainder of the rubric is the following stanzas.
9. Ibant magi, qua venerant,
Stellam sequentes previam,
Lumen requirunt lumine,
Deum fatentur munere.
11. Lavacra puri gurgitis
Cekstis agnus attigit ,
Peccata qui mundi tulit
Nos abluendo sustulit.
13. Novum genus potentie!
Aque rubescunt hydrie,
Vinumque iussa fundere
Mutavit unda originem.
See: Carl P. E. Springer, The Manuscripts of Sedulius - A Provisional Handlist (Philadelphia: American Philosophical Society, 1995), p. 14, n. 34 (Carl P. E. Springer Transactions of the American Philosophical Society New Ser., Vol. 85, No. 5 (1995), pp. i-xxii+1-244). See also Springer, "Sedulius' A Solis Ortus Cardine: The Hymn and Its Tradition, " Ephemerides Liturgicae 101 (1987), 69-75.
Note that the Bach Cantatas website, citing Grove's Music, states: "... the following four (beginning Katerva matrum personat, as above) for the Feast of the Holy Innocents." This would be verses 10-13, above, different from Springer's enumeration. See Sedulius.
As I do not read Latin, I am unable to provide a translation, nor have I located a translation on the World Wide Web.
A poem to the Holy Innocents can be found in Christmas-tide Poetry of John Keble.
Finally, the town of Hatillo, Puerto Rico, celebrates an unusual festival in conjunction with this feast day. "The Masks of Hatillo" is a 184 year old tradition in which inhabitants dress themselves in color as part of the celebration of the Masks Festival.
According to a published report in the newspaper El Vocero,
This tradition began in the town of Hatillo with the arrival of immigrants from the Canary Islands, where, on this date, it is customary to commemorate the massacre of the Holy Innocents, the children King Herod ordered executed so as to eliminate the newborn Child Jesus. As part of the festivity, it was customary to hold cavalcades where the riders, who portrayed the Roman soldiers at whose hands the Innocents died, dressed in colorful costumes and covered their faces with masks.
For more information, see the full post at Christmas International:
See, generally, December 28 - The Holy Innocents (Hone).