I refer readers to the earlier discussion on OCF 51 through 68, the introduction to the Vigil and Related Rites for adults. According to OCF 243, this vigil remains “the principal celebration” prior to the funeral liturgy. Remember that the vigil for the funeral of a child may, as it would for an adult, take the form of a Liturgy of the Word, or the Liturgy of the Hours (OCF 348ff).
OCF 244 treats the location of the vigil: it “may be celebrated … in the home of the deceased child, in the funeral home, parlor or chapel of rest, or in some other suitable place.” If celebrated in church, it should take place “at a time well before the funeral liturgy.” The reason given is sound: avoiding great length and repetition of Scripture readings.
The adult pattern of the Liturgy of the Word is “usually” maintained, according to OCF 245: reading, psalm, gospel reading, homily. One reading is a possibility, as it is for the vigil of an adult. That one reading should be taken from the Gospels–the same principle used in the Directory for Masses with Children. The funeral rites do offer prayers with alternate wordings–some for a baptized child, and some for a child who died before baptism. Song or silent prayer may conclude the vigil.
I do want to draw out the text for OCF 246:
The minister should adapt the vigil to the circumstances. If, for example, a large number of children are present or if the vigil is held in the home of the deceased child, elements of the rite may be simplified or shortened and other elements or symbols that have special meaning for those taking part may be incorporated into the celebration. If custom and circumstances suggest, a member or a friend of the family may speak in remembrance of the deceased child.
And again, as with the rest of the Roman Rite, the determination of adaptation is made not at the whim or preference of any of the ministers, but according to the best ministry practices for the mourners and the faith community.