This was a great discussion with the kids, and one in which I had to apologize for not having them baptized as infants.
Question #72: Does this outward washing with water itself wash away sins?
Answer: No, only Jesus Christ's blood and the Holy Spirit cleanse us from all sins ( Matt. 3:11; 1 Pet. 3:21; 1 John 1:7).
Question #73: Why then does the Holy Spirit call baptism the washing of rebirth and the washing away of sins?
Answer: God has good reason for these words. He wants to teach us that the blood and Spirit of Christ wash away our sins just as water washes away dirt from our bodies But more important,
he wants to assure us, by this divine pledge and sign, that the washing away of our sins spiritually is as real as physical washing with water (1 Cor. 6:11; Rev. 1:5; 7:14; Acts 2:38; Rom. 6:3-4; Gal. 3:27).
Question #74: Should infants, too, be baptized?
Answer: Yes. Infants as well as adults are in God's covenant and are his people. They, no less than adults, are promised the forgiveness of sin through Christ's blood and the Holy Spirit who produces faith. Therefore, by baptism, the mark of the covenant, infants should be received into the Christian church and should be distinguished from the children of unbelievers. This was done in the Old Testament by circumcision, which was replaced in the New Testament by baptism (Gen. 17:7; Matt. 19:14; Isa. 44:1-3; Acts 2:38-39; 16:31; Acts 10:47; 1 Cor. 7:14; Gen. 17:9-14; Col. 2:11-13).