22. … In the developments of medieval doctrine, the loss of the Beatific Vision (poena damni) was understood to be the proper punishment for original sin, whereas the “torments of perpetual hell” constituted the punishment for mortal sins actually committed.[47] In the Middle Ages, the ecclesiastical magisterium affirmed more than once that those “who die in mortal sin” and those who die “with original sin only” receive “different punishments”. [48]
23. Because children below the age of reason did not commit actual sin, theologians came to the common view that these unbaptised children feel no pain at all, or even that they enjoy a full natural happiness through their union with God in all natural goods (Thomas Aquinas, Duns Scotus). [49]
…
26. … Pius VI defended the right of the Catholic Schools to teach that those who died with the guilt of original sin alone are punished with the lack of the Beatific Vision (“punishment of loss”), but not sensible pains (the punishment of “fire”).
http://www.vatican.va/roman_curia/c...aith_doc_20070419_un-baptised-infants_en.html