I just realized everything I needed was in the original article by Fr. Brian W. Harrison, O.S. I linked to in my first post on this thread.
Here are some excerpts:
Pope Sixtus V, Apostlic Constitution Effaenatam of 29 October 1588:
For who would not detest a crime as execrable as this — a crime whose consequence is that not just bodies, but — still worse! — even souls, are, as it were, cast away? The soul of the unborn infant bears the imprint of God’s image! It is a soul for whose redemption Christ our Lord shed His precious blood, a soul capable of eternal blessedness and destined for the company of angels! Who, therefore, would not condemn and punish with the utmost severity the desecration committed by one who has excluded such a soul from the blessed vision of God? Such a one has done all he or she could possibly have done to prevent this soul from reaching the place prepared for it in heaven, and has deprived God of the service of this His own creature.
Pope Pius VI rejecting the Jansenist view that there is no Limbo stated that it is “false, rash, and injurious to Catholic schools”.
"At that time, the liberal theologians criticized by Fr. Le Blanc were beginning for the first time in Church history to raise the possibility of Heaven for all unbaptized infants — a totally novel hypothesis which was soon censured by the Holy Office under Pope Pius XII as unsound and “without foundation”.