francis - in the Prima set, it seems a good start to me : Four prayers: Sanctus, Doxology, Table Blessing, and Pater Noster Four Lingua Angelica songs: Dona Nobis Pacem, Chirstus Vincit, Adeste Fideles, and Resonet in Laudibus
Depending on your children, you might want to consider Hans Ørberg's Lingua Latina per se illustrata. It can be used with Ecclesiastical pronunciation.
Once pupils have some basics, they can start studying Fr. Lhomond's "Epitome historiæ sacræ", which is easier than his other book "De viris illustribus ...". I guess you can find second hand copies.
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