"Then Peter said to them, Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit. For the promise is to you and to your children, and to all who are afar off, as many as the Lord our God will call." Acts 2:38-39
Whole families were baptized, including children. Do you think some were baptized and other children in the same family were denied it because they were too young? That's an assumption, which doesn't stand up to further investigation. The Bible states that baptism is for the children too, with no age requirement specified, but if you need further proof, look no further than the witness of the early Christians who were the disciples of the apostles themselves. They all bear witness that baptism is the beginning of man's salvation as the scriptures teach, and that it's available to all men, women, and children.
I think this is the root of the problem. We have lost the correct undertanding of baptism. The purpose and value of repentance and baptism is to invite the presence of the Holy Spirit into one's heart, mind, and body. By a miracle of the Holy Spirit the waters are sanctified and made a way God chooses to work to cleanse us of sin and bring us into His flock. Who can deny this gift to children as well? They may later act in free will to depart from this grace, but this give them a good beginning.
Basil