The fact that unbaptized infants are conceived in a state of original sin and that they cannot be freed from original sin without baptism, and that infants are excluded from the beatific vision if they die unbaptized, is a solemnly defined dogma just as Our Lady’s Immaculate Conception. This is because no one can see the kingdom of God without the Sacrament of Baptism, and this includes infants, indeed it includes the whole human race. This is because of the original sin inherited from Adam.
The Catholic Church’s teaching is that children and infants who die without baptism descend immediately into Hell, but that they do not suffer the fires of Hell. They go to a place in Hell called the limbo of the children. The most specific definition of the Church that there is no way for an infant to be saved without the Sacrament of Baptism follows from one, Pope Eugene IV.Pope Eugene IV, Council of Florence, Session 11, Feb. 4, 1442: “Regarding children, indeed, because of danger of death, which can often take place, when no help can be brought to them by another remedy than through the sacrament of baptism, through which they are snatched from the domination of the Devil and adopted among the sons of God, it advises that holy baptism ought not be deferred for forty or eighty days, or any time according to the observance of certain people…”And from the Council of Carthage:Pope St. Zosimus, The Council of Carthage, Canon on Sin and Grace, 417 A.D.- "…that it might be understood that in the kingdom of heaven there will be some middle place or some place anywhere where the blessed infants live who departed from this life without baptism, without which they cannot enter into the kingdom of heaven, which is life eternal, let him be anathema.”This is defining that anyone who says that infants don’t need the “laver of rebirth” (sacramental baptism) to attain eternal life is a heretic.Pope Eugene IV, Council of Florence, “Letentur coeli,” Sess. 6, July 6, 1439: “We define also that… the souls of those who depart this life in actual mortal sin, or in original sin alone, go straightaway to hell, but to undergo punishments of different kinds.”Pope Pius VI, Auctorem fidei, Aug. 28, 1794:
“The doctrine which rejects as a Pelagian fable, that place of the lower regions (which the faithful generally designate by the name of the limbo of the children) in which the souls of those departing with the sole guilt of original sin are punished with the punishment of the condemned, exclusive of the punishment of fire, just as if, by this very fact, that these who remove the punishment of fire introduced that middle place and state free of guilt and of punishment between the kingdom of God and eternal damnation, such as that about which the Pelagians idly talk” – Condemned as false, rash, injurious to Catholic schools.
They go to a place in Hell where there is no fire. This perfectly conforms to all of the other solemn definitions of the Church, which teach that infants who die without water baptism descend into Hell, but suffer punishments different from those who die in mortal sin, they experience eternal separation from God.Pope Pius XI, Mit brennender Sorge (# 25), March 14, 1937: “‘Original sin’ is the hereditary but impersonal fault of Adam’s descendants, who have sinned in him. It is the loss of grace, and therefore eternal life, together with a propensity to evil, which everybody must, with the assistance of grace, penance, resistance and moral effort, repress and conquer.”
Pope Paul III, The Council of Trent, On Original Sin, Session V: “If anyone says that recently born babies should not be baptized even if they have been born to baptized parents; or says that they are indeed baptized for the remission of sins, but incur no trace of the original sin of Adam needing to be cleansed by the laver of rebirth for them to obtain eternal life, with the necessary consequence that in their case there is being understood a form of baptism for the remission of sins which is not true, but false: let him be anathema.”Here’s how the early Church father Pope St. Innocent expressed the teaching of tradition on this matter, against the Pelagian heretics:Pope St. Innocent, 414 A.D.: “…that even without the grace of Baptism infants are able to be endowed with the rewards of eternal life, is quite idiotic… But those who defend this for them without rebirth seem to me to want to quash Baptism itself, when they preach that infants already have what is believed to be conferred on them only through Baptism.”It must be remembered that it was Jesus Christ who laid down the requirement that all men, including infants, must be baptized for salvation: “Unless a man is born again of water and the Holy Ghost he cannot enter into the Kingdom of God”.