SemperFidelis, back to your original post.
The issue, I think, is this: We know that those who die in original sin go to hell eternally. You posit that this means that unbaptized children either go to Hell (of the damned) or Limbo (a “hell” of either natural beatitude or of “pain of loss” only or of both “pain of loss” and “pain of sense”, but the most mild “pain of sense” imaginable.) You therefore wish to retain the concept of Limbo.
I am inclined to do so as well (particularly the Thomistic concept of “natural beatitude”).
However, there is also another possibility which you seem to be overlooking: that unbaptized infants could somehow have original sin taken from them before they depart this world. If that can be so, then they won’t descend to Hell. The question then can infants receive sanctifying grace extra-sacramentally?
Some say yes. (Cardinal Cajetan, for instance). Others say no, and JohnGrey has been laying out that position.
But, my point is that the portions of the Council of Lyons and Florence that you quoted
in themselves do not lead to the conclusion that all unbaptized infants go to Hell (or Limbo). For that conclusion you a need middle term: namely that water baptism is the only way (and I mean ONLY - in the sense that God Himself never chooses some other way) an infant can be cleansed of original sin.
What do you think? Is that a fair summary of the problem?
VC