Outside the Sacrifice of the Mass and the use of the Roman Ritual, are there any Catholic historical traditions that are have been or are in use amongst the Catholic faithful for the feast of the Holy Innocents (December 28), either within religious communities or the domestic church?
Religious Customs in the Family: The Radiation of the Liturgy into Catholic Homes by Fr. Francis X. Weiser, S.J., mentions this regarding the Feast of the Holy Innocents (a.k.a "Childermas day"):
December 28, the feast of the Holy Innocents of Bethlehem, is a festive day for little children, according to ancient tradition. In Catholic families, December 28 should be the "feast of babies." The babies themselves cannot consciously celebrate it, of course; but the rest of the family can, with some appropriate observance like decorating the baby crib, having a party "for the baby," and/or blessing the baby with the Sign of the Cross; and everyone can pray to the Holy Innocents for their intercession, that God may bless the baby in body and soul.
Dom Guérenger's The Liturgical Year says this:
In Rome, the Station for the Feast of St. Stephen is in the Church dedicated to the holy Protomartyr, on Monte Celio; that for St. John is in the Basilica of St. Mary Major; today, the Station is made at St. Paul’s beyond the Walls, which possessed several of the bodies of the Holy Innocents. In the 16th century, Pope Xystus the Fifth caused a portion of these Relics to be translated to St Mary Major’s, and put near the holy Relic of our Lord’s Crib.
On the Feast of the Holy Innocents, it has became a custom, not only in the homes of the faithful, but also in convents and monasteries to serve an extra dish consisting of a white porridge (some kind of pabulum, usually cream of wheat with milk, sugar and cinnamon) to the youngest ones children in families and to the novices (a novice in some communities is any religious not yet in solemn vows) in religious houses, at the evening meal. This tradition is known as the Holy Innocents' Pabulum tradition. In know of some traditional (Extraordinary Rite) monastic communities that follow this tradition.
Other Holy Innocent customs include the superiors of some Religious Orders serving the noonday meal to the brethren. For example in some communities the abbot, prior, cellerar, and novice-master serve at table, while the sub-prior will do the table reading. The abbot of Westminster Abbey in Mission, BC serves tables of the brethren on this feast.
Just as the Magi fooled Herod, so this day is one of the most popular and entertaining Christmas traditions in Spain. December 28 is the day when everyone is allowed to play practical jokes and when it is customary to buy joke articles in Christmas markets like the one in the Plaza Mayor square in Madrid.