67 In this extremely delicate matter, if, all things considered, some private instruction is found necessary and opportune, from those who hold from God the commission to teach and who have the grace of state, every precaution must be taken. Such precautions are well known in traditional Christian education, and are adequately described by Antoniano cited above, when he says: Such is our misery and inclination to sin, that often in the very things considered to be remedies against sin, we find occasions for and inducements to sin itself. Hence it is of the highest importance that a good father, while discussing with his son a matter so delicate, should be well on his guard and not descend to details, nor refer to the various ways in which this infernal hydra destroys with its poison so large a portion of the world; otherwise it may happen that instead of extinguishing this fire, he unwittingly stirs or kindles it in the simple and tender heart of the child. Speaking generally, during the period of childhood it suffices to employ those remedies which produce the double effect of opening the door to the virtue of purity and closing the door upon vice.
Source: Divini Illius Magistri (Vatican.va)