"8. Everyone can pray, of this fact there can be no question. Everyone, therefore, has at hand and can make use of this all-important help, this daily nourishment of the missions. For these reasons you will act according to Our desires and will also do something in keeping with the religious spirit and feelings of the faithful, if you order that special prayers for the missions and for the conversion of the heathen to the true Faith be added, for example, to the Rosary of the Blessed Virgin or to the other prayers which are customarily recited both in the parish and other churches. It would be well, Venerable Brothers, to make a special point of inviting and encouraging children and the religious orders of women to take up this holy practice. We are particularly desirous that in all institutions, orphan asylums, parochial schools, colleges, and convents of Sisters there should daily arise to heaven the prayer that the Divine Mercy may descend upon so many unhappy beings, inhabitants of the densely populated pagan countries. Can the Heavenly Father refuse anything to the innocent and chaste who ask it of Him? On the other hand, such a pious practice leads to the hope that these children, who have been trained to pray for the conversion of the heathen from the first moment when the flower of charity begins to bud in their young and tender hearts, may, with the help of God, themselves receive a vocation for the apostolate, a vocation which if it is nurtured with care may perhaps in time supply capable workers for the mission field."
-Pope Pius XI, Rerum Ecclesiae