From Pius XI’s “On Christian Marriage” (Casti Connubii)

“16. The blessing of offspring, however, is not completed by the mere begetting of them, but something else must be added, namely the proper education of the offspring. For the most wise God would have failed to make sufficient provision for children that had been born, and so for the whole human race, if He had not given to those to whom He had entrusted the power and right to beget them, the power also and the right to educate them. For no one can fail to see that children are incapable of providing wholly for themselves, even in matters pertaining to their natural life, and much less in those pertaining to the supernatural, but require for many years to be helped, instructed, and educated by others. Now it is certain that both by the law of nature and of God this right and duty of educating their offspring belongs in the first place to those who began the work of nature by giving them birth, and they are indeed forbidden to leave unfinished this work and so expose it to certain ruin. But in matrimony provision has been made in the best possible way for this education of children that is so necessary, for, since the parents are bound together by an indissoluble bond, the care and mutual help of each is always at hand.”