Some thoughts found and offered ( I side on this question w/Aquinas, though w/Augstine on his vision of Heaven):
Summa Theologica Question 68, Article 3 "I answer that, In this matter we must make a distinction and see whether those who are to be baptized are children or adults. For if they be children, Baptism should not be deferred. First, because in them we do not look for better instruction or fuller conversion. Secondly, because of the danger of death, for no other remedy is available for them besides the sacrament of Baptism. On the other hand, adults have a remedy in the mere desire for Baptism, as stated above...
[edit] Latin Fathers
Saint Augustine of Hippo held that because of original sin, "such infants as quit the body without being baptized will be involved in the mildest condemnation of all. That person, therefore, greatly deceives both himself and others, who teaches that they will not be involved in condemnation; whereas the apostle says: 'Judgment from one offence to condemnation' (Romans 5:16), and again a little after: 'By the offence of one upon all persons to condemnation' (Romans 5:18)."[7]
The Council of North African bishops, which included Augustine of Hippo, held at Carthage in 418 did not explicitly endorse all aspects of Augustine's stern view about the destiny of infants who die without baptism, but the Latin Fathers of the fifth and sixth centuries did adopt his position, and it became a point of reference for Latin theologians in the Middle Ages.[8]
[edit] Medieval theologians
In the later medieval period, some theologians continued to hold Augustine's view. In the 1100s, Peter Abelard (1079 - 1142) said that these infants suffered no material torment or positive punishment, just the pain of loss at being denied the beatific vision. Others held that unbaptized infants suffered no pain at all: unaware of being deprived of the beatific vision, they enjoyed a state of natural, not supernatural happiness. This theory was associated with but independent of the term "Limbo of Infants", which was forged about the year 1300.[9]
If heaven is a state of supernatural happiness and union with God, and hell is understood as a state of torture and separation from God then, in this view, the Limbo of Infants, although technically part of hell (the outermost part, "limbo" meaning "outer edge" or "hem") is seen as a sort of intermediate state.
Saint Thomas Aquinas described the Limbo of Infants as an eternal state of natural joy, untempered by any sense of loss at how much greater their joy might have been had they been baptized. He argued that this was a reward of natural happiness for natural virtue; a reward of supernatural happiness for merely natural virtue would be inappropriate since, due to original sin, unbaptized children lack the necessary supernatural grace. In regards to baptism of desire, St Thomas Aquinas stated that only adults were capable of this,[10] and this view seemed to be accepted by the Council of Florence, which quotes St Thomas Aquinas in its Eleventh Session concerning baptism of infants
Council of Florence Session 11 (Bull Cantate Domino): "With regard to children, since the danger of death is often present and the only remedy available to them is the sacrament of baptism by which they are snatched away from the dominion of the devil and adopted as children of God, it admonishes that sacred baptism is not to be deferred for forty or eighty days or any other period of time..."
Other emergency means of baptism for children dying without sacramental baptism, such as prayer and the desire of the parents or the Church (vicarious baptism of desire - Cajetan), or the attainment of the use of reason in the moment of death, so that the dying child can decide for or against God (baptism of desire - H. Klee), or suffering and death of the child as quasi-Sacrament (baptism of suffering - H. Schell), are indeed possible, but their actuality cannot be proved from Revelation. Cf. Denzinger 712." Ludwig Ott, Fundamentals of Catholic Dogma, Book 2, Section 2, § 25 (p. 114 of the 1963 edition