The Church has taught and practiced from the very beginning that children, too, should be baptized. Sacred Scripture, the tradition of the Fathers, and the clear theology of Saint Thomas Aquinas provide weighty reasons for this.
1. Baptism is necessary for salvation.
Jesus himself says: “Unless one is born of water and the Spirit, he cannot enter the kingdom of God” (John 3:5). This necessity applies to all people, even the smallest, because they too bear original sin. Thomas Aquinas summarizes it as follows:
“Children too have original sin, which is taken away from them by baptism.” (Summa Theologiae III, q.68, a.9)
2. The Church believes on behalf of the child.
A baby cannot yet make a personal act of faith, but the Church intercedes on its behalf. The godparents and the community profess the faith of the Church at baptism, into which the child is received. Thomas says:
“Children are not baptized on the basis of their own act of faith, but on the faith of the Church, which brings them to the sacrament.” (STh III, q.68, a.9 ad 3)
3. The effect of baptism is objective: ex opere operato.
Infant baptism is not merely a subjective reception dependent on the feelings or consciousness of the recipient. Baptism works ex opere operato, that is: by the work having been performed itself, because Christ himself acts in it.
The grace of baptism is therefore objective, independent of the subjective psychological state of the recipient. Even if a child is not yet conscious of it, baptism truly removes original sin and grants sanctifying grace.
4. The new life in Christ is likewise objective.
Being born anew of water and the Spirit is not an inner feeling or a psychological insight, but a real, objective effect of baptism. Through baptism, the recipient is truly reborn as a child of God, even if he or she does not yet understand or feel this in the early stages of life. The Church states clearly:
“Baptism confers justification, the guilt of original sin is removed, and the person is reborn as a child of God.” (cf. Council of Trent, Sess. 7, Can. 5)
5. The early Church was unanimous on this.
Origen testifies: “The Church has received the tradition from the Apostles to baptize even little children.”
Cyprian of Carthage wrote after a synod in the year 252: “No one is to be excluded from baptism and the grace of God, not even the newborn child.”
Saint Augustine confirms: “The whole Church holds infant baptism; it is apostolic tradition.”
6. What about Tertullian?
Some opponents cite Tertullian, who thought it better to postpone baptism. But Tertullian was already on a rigorist path at that time and later became a heretic. The Church never adopted his personal opinion, but decisively contradicted it.
Summary:
Infant baptism is an objective act of Christ through the Church. It works ex opere operato: independent of subjective feelings, independent of psychological maturity. It removes original sin and truly, objectively, and indelibly makes the child a child of God. Being born anew in Christ is not merely an inner feeling, but a real new creation that happens through baptism alone.
Therefore:
“No one is to be excluded from baptism and the grace of God, not even the newborn child.” (Cyprian, Letter 64)
Scripture references:
Necessity of baptism: John 3:5
Promise for children: Acts 2:38–39
Household baptisms (including children): Acts 16:15; Acts 16:31–33; 1 Cor 1:16
Baptism as the new covenant sign like circumcision: Col 2:11–12
Jesus’ love for children: Mark 10:14
Mission command for all: Matt 28:19