6 We read of Eli the priest that he became displeasing to God on account of the sins of his children; and we are told that a man may not be made a bishop if his sons are loose and disorderly. On the other hand it is written of the woman that “she shall be saved in childbearing, if they continue in faith and charity and holiness with chastity.” If then parents are responsible for their children when these are of ripe age and independent; how much more must they be responsible for them when, still unweaned and weak, they cannot, in the Lord's words, “discern between their right hand and their left:” — when, that is to say, they cannot yet distinguish good from evil?
If you take precautions to save your daughter from the bite of a viper, why are you not equally careful to shield her from “the hammer of the whole earth”? to prevent her from drinking of the golden cup of Babylon? To keep her from going out with Dinah to see the daughters of a strange land? to save her from the tripping dance and from the trailing robe? No one administers drugs till he has rubbed the rim of the cup with honey; so, the better to deceive us, vice puts on the mien and the semblance of virtue.
Why then, you will say, do we read:— “the son shall not bear the iniquity of the father, neither shall the father bear the iniquity of the son,” but “the soul that sins it shall die”? The passage, I answer, refers to those who have discretion, such as he of whom his parents said in the gospel:— “he is of age...he shall speak for himself.” While the son is a child and thinks as a child and until he comes to years of discretion to choose between the two roads to which the letter of Pythagoras points, his parents are responsible for his actions whether these be good or bad.
But perhaps you imagine that, if they are not baptized, the children of Christians are liable for their own sins; and that no guilt attaches to parents who withhold from baptism those who by reason of their tender age can offer no objection to it. The truth is that, as baptism ensures the salvation of the child, this in turn brings advantage to the parents. Whether you would offer your child or not lay within your choice, but now that you have offered her, you neglect her at your peril.
I speak generally for in your case you have no discretion, having offered your child even before her conception. He who offers a victim that is lame or maimed or marked with any blemish is held guilty of sacrilege. How much more then shall she be punished who makes ready for the embraces of the king a portion of her own body and the purity of a stainless soul, and then proves negligent of this her offering?
Source: Letters (New Advent)