On this fourth Day of Christmas the Church specifically remembers an incident recorded in the Gospel of Matthew in the birth narratives. Recall that the Wise Men visited Herod first, presumably because they figured he would have known about the new-born King of the Jews. Well, for various reasons, Herod was never very sure of his grip on the throne, and so he was naturally threatened and scared. Known by both biblical as well as extra-Biblical sources as a very cruel ruler, he promptly had all the baby boys in Bethlehem under two years old executed. Thus, the Slaughter of the Holy Innocents.
The Collect for this Major Feast is, I think pretty direct:
We remember today, O God, the slaughter of the holy innocents of Bethlehem by King Herod. Receive, we pray, into the arms of your mercy all innocent victims; and by your great might frustrate the designs of evil tyrants and establish your rule of justice, love, and peace; through Jesus Christ our Lord, who lives and reigns with you and the Holy Spirit, one God, for ever and ever. Amen.
There is an excellent reflection on this day over at Thinking Anglicans. I commend it as better than what I might write.