We don’t question God’s mercy. How do you know it is either/or?
All things are possible with God.
“Babies dead without baptism go to Limbo, where they do not enjoy God, but neither do they suffer, because, having original sin alone, they do not deserve paradise, but neither do they merit hell or purgatory.” ~1905 Catechism of Pope Pius X,
Pope Martin V, Council of Constance, Session 15, July 6, 1415 - Condemning the articles of John Wyclif - Proposition 6: “Those who claim that the children of the faithful dying without sacramental baptism will not be saved, are stupid and presumptuous in saying this.” - Condemned
Pope St. Zosimus, The Council of Carthage, Canon on Sin and Grace, 417 A.D.- “It has been decided likewise that if anyone says that for this reason the Lord said: ‘In my Father’s house there are many mansions’ [John 14:2]: 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.” (Denz. 102, authentic addition to canon 2.)
Pope Paul III, The Council of Trent, On Original Sin, Session V, ex cathedra: “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.” (Denz. 791)
Pope Gregory X, Council of Lyons II, 1274: “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.” (Denz. 464)
Pope Eugene IV, Council of Florence, “Letentur coeli,” Sess. 6, July 6, 1439, ex cathedra: “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.” (Denz. 693)
Pope Pius VI, Auctorem fidei, Aug. 28, 1794:
“26. 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. (Denz. 1526)
Pope St. Innocent, 414 A.D.: “But that which Your Fraternity asserts the Pelagians preach, 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.” (Jurgens, The Faith of the Early Fathers, Vol. 3: 2016.)
St. Augustine, A.D. 415: “Anyone who would say that infants who pass from this life without participation in the Sacrament [of Baptism] shall be made alive in Christ truly goes counter to the preaching of the Apostle and condemns the whole Church, where there is great haste in baptizing infants because it is believed without doubt that there is no other way at all in which they can be made alive in Christ.” (Jurgens, The Faith of the Early Fathers, Vol. 3: 2016.)