One of the things that really freaks me out is how so many Christians invent, believe, and teach so many doctrines that simply have no scriptural authority. And this is one of them. Since the bible is silent (or at least unclear), we like to imagine that a kind, loving god would certainly act the way we think he should act. But that is not the God of the bible.
Nowhere in scripture can you find the concept of sinlessness before an "age of accountability" or any other free pass to heaven for any class of people including unborn babies who are aborted.
This question is divisive and explosive and lots of people get really angry about it. But the Bible is clear; even babies are conceived in iniquity and born in sin.
On this subject, I think R. C. Sproul Jr. has articulated the most intelligent, Biblically sound, and God-honoring answer I have ever read.
So, let God be God. You're not. Just believe Him when He speaks and trust Him when He is silent.