In Summa theologiae III, q. 69, a. 6, Saint Thomas takes up the question of whether children can be made partakers of grace through baptism even though they cannot yet exercise their wills. The four objections sum up the same objections that some Evangelicals and Baptists give today:

“To him that worketh not, yet believing in Him that justifieth the ungodly, his faith is reputed to justice according to the purpose of the grace of God.”

But a child believeth not “in Him that justifieth the ungodly.

Thomas Aquinas cites a beautiful passage from Augustine in response to these objections:

As Augustine says (Serm. clxxvi): “Mother Church lends other feet to the little children that they may come; another heart that they may believe; another tongue that they may confess.” So that children believe, not by their own act, but by the faith of the Church, which is applied to them: by the power of which faith, grace and virtues are bestowed on them.

Mother Church lends the feet, heart, and the tongue to the infants. It may come as a surprise to Evangelicals, but Catholics do actually believe in “believer’s baptism”. The Sacred Scriptures reveal that there can only be “believer’s baptism”.

When a baby is baptized, he is infused with the virtue of faith and thus he becomes a “baptized believer”. Faith is not a feeling – it is a divinely infused habit of the soul (STh II-II q. 6, a. 1). The baby becomes a real believer. It is not “faith reckoned” but actually faith that is found in the baby. Must this faith grow? Yes. Must this faith be confessed? Yes. Must this faith be understood and articulated? Yes. All of these things apply equally to adult believers who receive baptism.