I made the assumption that your friend was asking from the point of view of many protestants that baptism is simply a symbol of ones faith, and had no effect on the soul.

Let’s say the child was not baptized. There is a concept (not a defined dogma of the Catholic Church) of Limbo. Limbo is a pious belief, that some theologians have proposed. In the concept of Limbo a child who dies before the age of reason, without baptism is granted perfect natural happiness. However there are other Catholic Theologians who say that the Child like a pagan or someone who had never been given the opportunity in life to know and accept Jesus is given the information about Jesus, and the plan of salvation and is then given the choice to accept or reject the truth.

Many Protestants say the only way to salvation is by accepting Jesus as ones Lord and Personal Savior. If you did not get the chance, (especially those who believe in absolute predestination) you go to Hell, no other options.

As Catholics we believe in God’s mercy, and that He will judge us based on what we know, not in an intellectual sense. but rather if we did not get a chance to hear the Gospel in this life, either we are informed of it before our Judgement, and make our determination then, or possibly we are judged based on natural law, (ie all societies believe stealing, murder and adultary are wrong).