Some may think that Limbo is an hypothesis dreamed up by scholars of the Middle Ages, but this is far from the truth. Limbo is a conclusion reached by many Christian minds throughout the centuries trying to understand and clarify God's justice, Original Sin which deprived mankind of God's grace and eternal life and the need for Baptism to restore this life as expressed by Christ to Nicodemus, "Amen, amen, I say to you, no one can enter the kingdom of God without being born of water and Spirit." (Jn 3:5) St. Augustine reflecting on the Scriptures says the the following saying of Christ are just as universal, "Everyone who acknowledges me before others I will acknowledge before my heavenly Father." (Mt 10:32) "For whoever wishes to save his life will lose it, but whoever loses his life for my sake will find it." (Mt 16:25) Implied in these verses is "baptism of desire" and "baptism of Blood". Baptism of desire means that even those who do not know Christ will be saved if they seek the truth striving to do God's will in accordance with their conscience. (Cath. of Cath. Church #1216)
But, Christians began to ask: "What happens to children who die before the use of reason without baptism?"
St. Gregory of Nazianzus (c.325-389 AD), Father and Doctor of the Church stated the following: " "It will happen, I believe ... that those last mentioned [infants dying without baptism] will neither be admitted by the just judge to the glory of Heaven nor condemned to suffer punishment, since, though unsealed [by baptism], they are not wicked. ... For from the fact that one does not merit punishment it does not follow that one is worthy of being honored, any more than it follows that one who is not worthy of a certain honor deserves on that account to be punished." [Orat., xl, 23]20
St. Augustine of Hippo (354-430 AD) thought that unbaptized infants went to Hell but experienced a very mild type of suffering. This was unacceptable to many.
"St. Thomas was the first great teacher who broke away completely from the Augustinian tradition on this subject, and relying on the principle, derived through the Pseudo-Dionysius from the Greek Fathers, that human nature as such with all its powers and rights was unaffected by the Fall (quod naturalia manent integra), maintained, at least virtually, what the great majority of later Catholic theologians have expressly taught, that the limbus infantium [limbo of infants]is a place or state of perfect natural happiness."
So, many Christian thought throughout the centuries considered the possibility of heaven for infants and rejected it.