Objection 1. It would seem that the limbo of children is the same as the limbo of the Fathers. For punishment should correspond to sin. Now the Fathers were detained in limbo for the same sin as children, namely for original sin. Therefore the place of punishment should be the same for both.
Objection 2. Further, Augustine says (Enchir. xciii): "The punishment of children who die in none but original sin is most lenient." But no punishment is more lenient than that of the holy Fathers. Therefore the place of punishment is the same for both.
On the contrary, Even as temporal punishment in purgatory and eternal punishment in hell are due to actual sin, so temporal punishment in the limbo of the Fathers and eternal punishment in the limbo of the children were due to original sin. If, therefore, hell and purgatory be not the same it would seem that neither are the limbo of children and the limbo of the Fathers the same.
I answer that, The limbo of the Fathers and the limbo of children, without any doubt, differ as to the quality of punishment or reward. For children have no hope of the blessed life, as the Fathers in limbo had, in whom, moreover, shone forth the light of faith and grace. But as regards their situation, there is reason to believe that the place of both is the same; except that the limbo of the Fathers is placed higher than the limbo of children, just as we have stated in reference to limbo and hell (5).
Reply to Objection 1. The Fathers did not stand in the same relation to original sin as children. For in the Fathers original sin was expiated in so far as it infected the person, while there remained an obstacle on the part of nature, on account of which their satisfaction was not yet complete. On the other hand, in children there is an obstacle both on the part of the person and on the part of nature: and for this reason different abodes are appointed to the Fathers and to children.
Reply to Objection 2. Augustine is speaking of punishments due to some one by reason of his person. Of these the most lenient are due to those who are burdened with none but original sin. But lighter still is the punishment due to those who are debarred from the reception of glory by no personal defect but only by a defect of nature, so that this very delay of glory is called a kind of punishment.
Source: Summa Theologica (New Advent)