These next two sections are all rubrics. In 297, a minimum of one reading, presumably the Gospel, is designated. If two readings are utilized, then a psalm “or a song” should be used between the readings. Usually when the rite mentions a “song,” the example given is a psalm. I don’t see any reason why a parish wouldn’t use a psalm–it’s just good liturgical practice. Plus we lack no decent number of psalm settings in music collections for children.
Six choices for readings are given: Ezekiel 36:25-28 (new heart, new spirit) or Isaiah 1:16-18 (cleansing of sin) or Mark 1:1-5, 14-15 (repent!) or Mark 2:1-12 (Jesus heals the paralyzed man) or Luke 15:1-7 (lost sheep) or 1 John 1:8-2:2 (Jesus is savior). Shorter versions of the scrutiny gospels are also given as options.
The Psalms and given refrains are 23 (The Lord is my shepherd; there is nothing I shall want), 27 (The Lord is my light and my salvation), 32 (Happy are those whose sins are forgiven) and 89 (Forever I will sing the goodness of the Lord) or any psalms in the Lectionary’s section on Christian Initiation apart from the Easter Vigil.
RCIA 298 designates the “sacred texts” to be explained in a “short homily.” I presume that means not just the readings, but also the prayers of the penitential rite. The rest of the direction:
During the homily or immediately after it, the celebrant prepares all those in the assembly for conversion and repentance by speaking to them of appropriate themes, then pausing for periods of silent reflection.
If the assembly includes baptized children who will receive the sacrament of penance for the first time, the celebrant turns to them and invites them to show by some external sign their faith in Christ the Savior and their sorrow for their sins.