Objection 1. It seems that children of Jews or other unbelievers should be baptized against the will of their parents. For it is a matter of greater urgency to rescue a man from the danger of eternal death than from the danger of temporal death. But one ought to rescue a child that is threatened by the danger of temporal death, even if its parents through malice try to prevent its being rescued. Therefore much more reason is there for rescuing the children of unbelievers from the danger of eternal death, even against their parents' will.
Objection 2. The children of slaves are themselves slaves, and in the power of their masters. But Jews and all other unbelievers are the slaves of kings and rulers. Therefore without any injustice rulers can have the children of Jews baptized, as well as those of other slaves who are unbelievers.
Objection 3. Further, every man belongs more to God, from Whom he has his soul, than to his carnal father, from whom he has his body. Therefore it is not unjust if the children of unbelievers are taken away from their carnal parents, and consecrated to God by Baptism.
On the contrary, It is written in the Decretals (Dist. xlv), quoting the council of Toledo: "In regard to the Jews the holy synod commands that henceforward none of them be forced to believe: for such are not to be saved against their will, but willingly, that their righteousness may be without flaw."
I answer that, The children of unbelievers either have the use of reason or they have not. If they have, then they already begin to control their own actions, in things that are of Divine or natural law. And therefore of their own accord, and against the will of their parents, they can receive Baptism, just as they can contract marriage. Consequently such can lawfully be advised and persuaded to be baptized.
If, however, they have not yet the use of free-will, according to the natural law they are under the care of their parents as long as they cannot look after themselves. For which reason we say that even the children of the ancients "were saved through the faith of their parents." Wherefore it would be contrary to natural justice if such children were baptized against their parents' will; just as it would be if one having the use of reason were baptized against his will. Moreover under the circumstances it would be dangerous to baptize the children of unbelievers; for they would be liable to lapse into unbelief, by reason of their natural affection for their parents. Therefore it is not the custom of the Church to baptize the children of unbelievers against their parents' will.
Reply to Objection 1. It is not right to rescue a man from death of the body against the order of civil law: for instance, if a man be condemned to death by the judge who has tried him, none should use force in order to rescue him from death. Consequently, neither should anyone infringe the order of the natural law, in virtue of which a child is under the care of its father, in order to rescue it from the danger of eternal death.
Reply to Objection 2. Jews are slaves of rulers by civil slavery, which does not exclude the order of the natural and Divine law.
Reply to Objection 3. Man is ordained unto God through his reason, by which he can know God. Wherefore a child, before it has the use of reason, is ordained to God, by a natural order, through the reason of its parents, under whose care it naturally lies, and it is according to their ordering that things pertaining to God are to be done in respect of the child.
Source: Summa Theologica (New Advent)