I once set myself to gathering a good deal of quotes on the subject after listening to an Audio Sancto sermon on Limbo which basically condemned the ITC and its paper on the matter.
Limbo is the lighter view, in many ways, historically. It is better than Hell proper.
Here from my notes, I have not looked at these in awhile so do not recall much, I have some of the source citations second hand I think, but do not doubt them, fwif:
'Whoever says that infants are alive in Christ even when they depart this life without being baptized is really both opposing the Apostolic preaching and condemning the whole Church which runs hastily with infants to the baptismal font because it is believed without any doubt that otherwise these infants cannot possibly be alive in Christ.'
St. Augustine, Father and Doctor of the Church, 'Doctor of Grace' (a letter to St. Jerome (no. 27))
'The common teaching of the scholastic theologians is the within the earth there are four inner chambers: one for the damned, another for those being purged of sin, a third for those infants who have died without receiving Baptism, and a fourth which is now empty but once held those just men who died before the passion of Christ.'
St. Robert Bellarmine (1542-1621), Doctor of the Church
'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.'
St. Gregory Nazanzien, Father and Doctor of the Church, [Orat., xl, 23]
'If you want to be a Catholic do not believe, do not say, do not teach that infants carried off by death before being baptized can obtain the remission of original sin."
St. Augustine, Father and Doctor of the Church 'Doctor of Grace' (III de Anima)
Q. Where do infants go who die without baptism?
A. Infants who die without baptism go to Limbo, where they do not enjoy the sight of God but also do not suffer, this is because having original sin and this alone they do not merit Heaven but neither do they merit purgatory or Hell.
- Catechism of Christian Doctrine
'For there be some that are withdrawn from the present light, before they attain to shew forth the good or evil deserts of an active life. And whereas the Sacraments of salvation do not free them from the sin of their birth, at the same time that here they never did aright by their own act; there they are brought to torment. And these have one wound, viz. to be born in corruption, and another, to die in the flesh. But forasmuch as after death there also follows, death eternal, by a secret and righteous judgment "wounds are multiplied to them without cause." For they even receive everlasting torments, who never sinned by their own will. And hence it is written, Even the infant of a single day is not pure in His sight upon earth. Hence "Truth" says by His own lips, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God. Hence Paul says, We were by nature the children of wrath even as others.
He then that adding nothing of his own is mined by the guilt of birth alone, how stands it with such an one at the last account, as far as the calculation of human sense goes, but that he is "wounded without cause?" And yet in the strict account of God it is but just that the stock of mortality, like an unfruitful tree, should preserve in the branches that bitterness which it drew from the root. Therefore he says, For He shall break me with a tempest, and multiply my wounds without cause. As if reviewing the woes of mankind he said in plain words; "With what sort of visitation does the strict Judge mercilessly slay those, whom the guilt of their own deeds condemns, if He smites for all eternity even those, whom the guilt of deliberate choice does not impeach?"'
Pope St. Gregory the Great
.. Basically, I see the current climate an extrapolation of the universal or near universal salvation theme in regards to Limbo.
First one gets rid of the place, then one extends mercy to the extent it does not exist as a state of being, and condemns the past saints and popes statements as antiquated and lacking in hope and mercy.
But, it has struck me that if infants by default went to Heaven, we would have heard about it long before now. Who would not wish to say it -- if it could be said?