Baptism makes us children of God and heirs of heaven, (not creation, not birth does this). In addition, baptism gives sanctifying grace which informs both the intellect and the will, the higher faculties. Without baptism, these higher faculties are not illuminated by grace.
Although we can come to know God somewhat through the glory of His creation, we cannot know God intimately without the participation of His divine existence, which is sanctifying grace. Baptism, therefore, lifts the intellect and will out of darkness. If a child is not baptized, of course, God gives each person sufficient grace for salvation, as soon at they can reason and appropriate this grace.
All receive this grace, and if the person refuses this grace, they fall into further darkness, stopping the searching of the intellect and interfering with the will’s ability to respond to the enlightened intellect.
This is all the long teaching of the Catholic Church. Baptism enlightens the intellect and strengthens the will, allowing one to have an intimate relationship with God.
Children who are not baptized will fall into mortal sin very quickly following the entrance into the age of reason. Sad, but true.
God can give a special grace outside of baptism, but this is rare. And, this fact is why certain people in this world turn to violence and religious fundamentalism, as their intellects and wills are not illumined by God’s grace, which is a participation in His Life.