Babies who are not baptized will not go to hell because they are not guilty of anything. God will judge people on the basis of what they did in light of what they knew.
Babies have not done anything wrong because they do not know the difference between right and wrong. And so they have not sinned.
Furthermore, Jesus said, “Their angels always see the face of My Father who is in heaven” (Matthew 18:10).
Remember also, original sin is a tendency to sin, not an act of sin. Original sin is not original guilt. To be guilty before God, a child has to understand that what he or she is doing is wrong.