Catechism of the Catholic Church

Following St. Paul, the Church has always taught that the overwhelming misery which oppresses men and their inclination toward evil and death cannot be understood apart from their connection with Adam's sin and the fact that he has transmitted to us a sin with which we are all born afflicted, a sin which is the "death of the soul." Because of this certainty of faith, the Church baptizes for the remission of sins even tiny infants who have not committed personal sin. (2606, 1250)