Today, on this Fourth day of Christmastide, we hail the New-Born Savior as the Lord, the King of Martyrs [Dominus, Rex Martyrum], as we greet at the Crib of Christ the Holy Innocents.
As the 1962 Missal introduces:
It was because Herod believed the words of the Magi and of the High Priest whom he consulted that he sees as a rival in the Infant of Bethlehem and with jealousy pursues the Child, born King of the Jews. It is this God-King that the Holy Innocents by dying confess. Their passion is the exaltation of Christ. 
Dom. Prosper Guéranger adds:
Herod intended to include the Son of God amongst the murdered Babes of Bethlehem. The Daughters of Rachel wept over their little ones, and the land streamed with blood; the Tyrant’s policy can do no more: it cannot reach Jesus, and its whole plot ends in recruiting an immense army of Martyrs for heaven. These Children were not capable of knowing what an honor it was for them to be made victims for the sake of the Saviour of the world; but the very first instant had gone through this world without knowing it, and now that they know it, they possess an infinitely better. God showed here the riches of his mercy: he asks them but a momentary suffering, and that over, they wake up in Abraham’s Bosom: no further trial awaits them, they are in spotless innocence, and the glory due to a soldier who died to save the life of his prince belongs eternally to them. [Guéranger 278]
For out of the mouth of infants and of sucklings, O God, Thou hast perfected praise, because of Thine enemies [Ps 8. 3] the Introit rings.
May we ask always for the prayers of these most blameless Martyrs.