First, given that all humans have sinned in Adam, from the hand of God, not men, every human (i.e. babies) deserves death and the wrath of God (Romans 5:12-14). This is why we (even babies) die, we/they sinned in Adam (Rom. 6:23). But, via election babies who die before their brains mature, could still receive salvation.

So, how could a baby go to heaven, if God were to elect a soul that dies in infancy?

I have an idea:

• God has thoughts without a physical brain
• Our brain functions as the home of the thoughts of our soul
• The soul is given truth that the brain reflects and uses
• The Spirit of God gives our soul gospel truth, that out brain processes and produces repentance and faith
  • Ultimately, there is a connection with the brain and the soul
• In the intermediate state, we are still ourselves while we wait for our resurrection bodies. So, knowledge is obtained not by the brain, but the soul.
  • We should not become materialist or naturalist when it comes to the super natural knowledge, it comes from a being that has no physical brain.
• At some point in time, for the elect, the soul is saved, regardless of age. Souls don't develop, but the body that a soul uses, does. This effects the demonstration (fruit) of a saved soul.

Biblical support: 2 Tim. 2:25, Rom. 8, etc