114 Consequently, both those who are now thinking of entering upon this sacred married state, as well as those who have the charge of educating Christian youth, should, with due regard to the future, prepare that which is good, obviate that which is bad, and recall those points about which We have already spoken in Our encyclical letter concerning education: "The inclinations of the will, if they are bad, must be repressed from childhood, but such as are good must be fostered, and the mind, particularly of children, should be imbued with doctrines which begin with God, while the heart should be strengthened with the aids of divine grace, in the absence of which, no one can curb evil desires, nor can his discipline and formation be brought to complete perfection by the Church. For Christ has provided her with heavenly doctrines and divine sacraments, that He might make her an effectual teacher of men."
Source: Casti Connubii (Vatican.va)