The reasoning given by church leaders for baptizing infants is that it is a Christian substitute for Jewish circumcision.
To be consistent, babies must be baptized on the eighth day and can only be boys. And, everyone who works for that family must also have their baby boys circumcised or be fired. (See Genesis 17:12,13).
The only time baptism is mentioned in connection with circumcision is this [capitals mine]:
"In him you were also circumcised, in the putting off of the sinful nature, NOT with a circumcision done BY THE HANDS OF MEN but with the circumcision done by Christ, having been BURIED WITH HIM IN BAPTISM and raised with him through YOUR FAITH in the power of God, who raised him from the dead.
"When you were dead in your sins and in the uncircumcision of your sinful nature, God made you alive with Christ. He forgave us all our sins, having canceled the written code [Old Testament] with its regulations, that was against us and that stood opposed to us; he took it away, nailing it to the cross" (Colossians 2:11-14). This scripture refers to someone with faith and a form of circumcision not performed by men, which would eliminate babies and baptism which is performed by men.
Further, whenever the apostles argued with Jewish Christians not to circumcise their babies as a religious rite, never did he tell them to baptize their babies instead (Acts 15:1-21; 1 Corinthians 7:17-20; Galatians 2:3-5; 5:1-12; 6:12-16).
Never in the scriptures is there a story saying directly that a baby was baptized. None. Preachers who practice this will say it is inferred when entire households were baptized. But if you investigate these, you will find those entire households also believed. Can infants believe?
The scripture most cited for infant baptism is in the Old Testament where David said in Psalm 51:5, "Surely I was sinful at birth, sinful from the time my mother conceived me."
David had just had to admit he had committed adultery and she was now pregnant. It nearly killed him. And while he was at it, he referred to the adulterous situation under which his lineage was born, as though "It has happened again."
Why? Because Deuteronomy 23:2, part of the Law of Moses David lived under, says, "No one born of a forbidden marriage nor any of his descendants may enter the assembly of the Lord, even down to the tenth generation." What was a forbidden marriage? Among others, it was one between a father and daughter-in-law (Leviticus 18:15).
Genesis 38 says that Judah's son married Tamar and then died. But for various reasons, his brothers refused to carry on their deceased brother's name as commanded in Deuteronomy 24:5-10. So she dressed up like a prostitute, and when Judah, newly widowed, saw her, he went to bed with her. As a result, she had an illegitimate son named Perez, David's ancestor.
Matthew 1:3-6 gives the lineage of David. Counting the generations between Perez and David reveals it to be ten generations (remember Deuteronomy 23:2 regarding this?). In this sense, David was conceived in sin. (And, by the way, it was his son, Solomon of the 11th generation who built the temple.)
All babies and little children are as saved as adult Christians. Hebrews 1:14 says, "Are not all angels ministering spirits sent to serve those who will inherit salvation?" And Jesus himself said in Matthew 18:10, "'See that you do not look down on one of these little ones. For I tell you that their angels in heaven always see the face of my Father in heaven.'" Did he say only baptized children? Never.
Further, Jesus said in Matthew 19:14, "Let the little children come to me, and do not hinder them, for the kingdom of heaven belongs to such as these." He did not say, for the kingdom of heaven belongs to children after they are baptized. He said the kingdom of heaven right now belongs to them.
Never did David believe a baby was doomed to hell. This psalm was written when he found out Bathsheba was pregnant by him outside of wedlock. The account of that event is in 2 Samuel 11 and 12. After the baby was born, he got sick and died seven days later, too early to be scripturally circumcised. Did David believe his uncircumcised baby went to hell? No. He said, "'Can I bring him back again? I will go to him, but he will not return to me'" (2 Samuel 12:23).