The Penalty for Original SIn is first and foremost death of the soul in the loss of sanctifying grace, enslavement to the Devil, having the nature of Adam’s guilt imputed to us by procreation, that is, generation, and being incapable of doing anything that is supernaturally pleasing to God. We are also born enemies of God, under his wrath, and condemned, but not directly by God, our fallen nature dondemns us. As Pope St. Gregory I says: “Even the infant of a single day is not pure in his sight.” Oh, and The eternal penalty for original sin is condemnation to hell and loss of the beatific vision, but those who die in original sin alone and who are punished in hell are punished differently than those who die in Mortal sin. But this difference is not clear. It could be merely a qualitative difference (Deprivation of the vision of God alone, without the torment of hellfire, but the torment of the lack of being in God’s presence), a quantitative difference (Augustine’s Infant damnation, though he held they are punished with the lightest of punishments), or both (Lack of the Vision of God, without any Kind of positive torment, a la Peter Abelard)
As Far as Ecumenical Councils go, you really want to read Session 5 of the council of Trent, as well as the beginning of Session 6, and The Bull Cantate Domino By Pope Eugene IV, given at the Ecumenical COuncil of Florence, as Well as the Canons of Florence and the council of Lyons II, The Council of Orange II in the 6th century ( a regional council given ecumenical status by the second council of Nicea),
and the Council of Carthage XVI, which was approved and ratified by Pope Zosimus and whose findings he published in his tractoria, which he had all the Bishops sign under pain of excommunication, and also ratified by the Council of Ephesus. There it clearly states the penalty for dying in original sin alone is the absolute exclusion form any form of happiness anywhere. And Pope St. Zosimus said this is to be taken as the Apostolic See’s own faith.
That help? You can also see my thread on limbo.