I understand what you are saying here"I trust in the MERCY of God to welcome infants into Heaven, but I would never speak FOR God and claim that i know in any way who IS in Heaven and who is not."
But by the Bible we can KNOW that God is righteous and will always therefore do right, for those who are unable to make free will choices that result in sin: there is no question in my mind but that a perfect God wouldnt send people to hell who have no ability to choose. When we are offered a temptation and we KNOW that to indulge is wrong and we do it anyway, this is sin. If a person is truly incapable of knowing right from wrong how can they be guilty of sin?
I am not speaking for god that seems to be the purview of the UBER bosses in Rome, they repeatedly make pronouncements as if they speak for God.
But, as for other individuals, I can know by Gods word that certain people dont go to heaven. So if I see a person who is an active homosexual for example I can confidently declare that if they die as they are now, they will NOT go to heaven. This is from Gods word, so therefore I am not speaking for him only sharing with that person what GOD has said.
And I understand what you are saying about getting info from the horses mouth as it were, but the little bit of the Catechism I have read didnt have clear biblical support listed along with it, if there is a resource that shows both I will use it. But I just wont study the Catechism on its own.
And as far as the wikipedia goes I admitted that it is often not the most trustworthy site, that being said from the dictionary you can see that limbo and purgatory are almost exclusively Catholic concepts.
please see this link to limbo
http://www.bartleby.com/61/19/L0171900.html
and this to purgatory
http://www.bartleby.com/61/80/P0668000.html