I know what you mean, Beads, because it does seem a bit ambiguous.
At this point, I don't have any verses to back me up, but here's what I believe:
All babies are born inherently evil. We get it from being human.
A three month old child can sin -- babies are essentially selfish.
A three month old child cannot understand the concept of sin, of grace, faith, or Jesus Christ. Until it can understand, and I would think that it's possible to understand something of Christ's deity when a child is quite young, it won't be held accountable.
I know God cannot accept evil into Heaven, but Christ died for all, and God gives life and takes it away. It would seem just, then, that everyone gets an opportunity to accept Christ at some point (those who have not the gospel have Creation-- Romans) and those that do not -- the very young, or unborn -- are premitted into Heaven by default.
With this issue, it may not be as well-grounded in Scripture as I want, but it does correspond to God's just nature.