Well… your conclusion is reasonable, but the path you take in getting there is certainly … novel.
The Church has never explicitly interpreted this verse thus. I think it would be just as reasonable to suggest that rather than meaning “all children go to heaven”, Jesus meant, “it’s wrong to keep children from belief in me, since they (in their innocence) are who should be believing and going to heaven!”. In fact, I think that this verse has better application in the context of infant baptism than it does in a novel theory of “salvation by virtue of age.”
(Nevertheless, we would say that a child who has been baptized but dies before the so-called “age of reason” is incapable of mortal sin, and therefore, will be saved.)
I think that this interpretation doesn’t do justice to the actual text in Scripture. In Mt 19:14, the word used is ‘παιδία’ (paidia), or literally, “little children”. However, in Mt 18:10, the word used is ‘μικρῶν’ (mikron), or “little (ones)”. So, equating the two doesn’t exactly hold up to reason. As further evidence of this, please note that Jesus uses the term “little ones” in many contexts, and does not mean “children” in these verses (Mt 10:42, Mt 18:6).
So, while I think you’re moving in a reasonable direction, the ‘proof-texts’ that you utilize aren’t saying quite what you say they’re saying.
No, no objections… but not for the reasons you’ve presented. See the Vatican document The Hope of Salvation for Infants who Die without Being Baptized. The arguments presented there also hold for those who die prior to birth (see paragraph 2 of this document, which states, “the number of infants who die unbaptized is growing greatly… partly a consequence of in vitro fertilization and abortion”).
This document, then, makes the claim that there are “strong grounds for hope that God will save infants when we have not been able to do for them what we would have wished to do, namely, to baptize them into the faith and life of the Church.”