Catholics are often accused of teaching a works based Gospel in which one must earn God’s grace and love. Yet, we take the least capable of earning anything (except maybe by their cuteness) and entrust them to the bountiful grace and mercy of God. We do this because we know salvation comes from the grace bestowed upon us by the mysterious promises of God. Catholics even get the word for sacrament from this. Sacramentum (oath) is one of the two Latin words that was used to translate the Greek word musterion. The other latin word is mysterium, meaning mystery. The sacraments are mystery and oath, a reality captured by the East calling them the mysteries and the West calling them the Sacraments. 
We do this in harmony with the early church:
St. Irenaeus (disciple of Polycarp who was a disciple of St. John, you know the guy who wrote about being born again by water and spirit) – “Christ came to save all through Himself; all I say, who are born anew (or baptized) through Him – infants and little ones, boys and youths, and aged persons” (Lib. II. adr. Haer.).
Origen – “The Church received from the Apostles, to give baptism even to infants” (In Ep. ad Rom.).
An African Council in 253 attended by St. Cyprian in response to the question of whether to wait until at least the 8th day after birth to Baptize – “As to what regards the baptism of infants, … we all judged the mercy and grace of God should be denied to no human being from the moment of his birth. If even to the greatest delinquents the remission of sins is granted, how much less should the infant be repelled, who, being recently born according to Adam, has contracted at his first birth the contagion of the ancient death” (Epis. ad Fidum). (The above quotes were taken from James Cardinal Gibbons’ book Faith of Our Fathers (1917) pages 221-222.)