I answer that, As stated above (Article [2], ad 1), the religious vow is twofold. One is the simple vow consisting in a mere promise made to God, and proceeding from the interior deliberation of the mind. Such a vow derives its efficacy from the divine law. Nevertheless it may encounter a twofold obstacle. First, through lack of deliberation, as in the case of the insane, whose vows are not binding [*Extra, De Regular. et Transeunt. ad Relig., cap. Sicut tenor]. The same applies to children who have not reached the required use of reason, so as to be capable of guile, which use boys attain, as a rule, at about the age of fourteen, and girls at the age of twelve, this being what is called "the age of puberty," although in some it comes earlier and in others it is delayed, according to the various dispositions of nature. Secondly, the efficacy of a simple vow encounters an obstacle, if the person who makes a vow to God is not his own master; for instance, if a slave, though having the use of reason, vows to enter religion, or even is ordained, without the knowledge of his master: for his master can annul this, as stated in the Decretals (Dist. LIV, cap. Si servus). And since boys and girls under the age of puberty are naturally in their father's power as regards the disposal of their manner of life, their father may either cancel or approve their vow, if it please him to do so, as it is expressly said with regard to a woman (Num. 30:4).
Accordingly if before reaching the age of puberty a child makes a simple vow, not yet having full use of reason, he is not bound in virtue of the vow; but if he has the use of reason before reaching the age of puberty, he is bound, so far as he is concerned, by his vow; yet this obligation may be removed by his father's authority, under whose control he still remains, because the ordinance of the law whereby one man is subject to another considers what happens in the majority of cases. If, however, the
child has passed the age of puberty, his vow cannot be annulled by the authority of his parents; though if he has not the full use of reason, he would not be bound in the sight of God.
The other is the solemn vow which makes a man a monk or a religious. Such a vow is subject to the ordinance of the Church, on account of the solemnity attached to it. And since the Church considers what happens in the majority of cases, a profession made before the age of puberty, however much the person who makes profession may have the use of reason, or be capable of guile, does not take effect so as to make him a religious (Extra, De Regular., etc. cap. Significatum est.).
Nevertheless, although they cannot be professed before the age of puberty, they can, with the consent of their parents, be received into religion to be educated there: thus it is related of John the Baptist (Lk. 1:80) that "the child grew and was strengthened in spirit, and was in the deserts." Hence, as Gregory states (Dial. ii, 3), "the Roman nobles began to give their sons to the blessed Benedict to be nurtured for Almighty God"; and this is most fitting, according to Lam. 3:27, "It is good for a man when he has borne the yoke from his youth." It is for this reason that by common custom children are made to apply themselves to those duties or arts with which they are to pass their lives.