Oikos (household) evangelism, led to household baptisms in the book of Acts. The father got saved and the whole household (wife, children, and perhaps servants) got baptized. Nothing in the text indicates that the father carefully led each of his family members to Christ before they were baptized. As far as we know, all of these family members were baptized just as infants are today, in some of our denominational traditions, before they understood the gospel messege and have repented and believed. Read the story in Acts 16.
Household baptisms also occurred on the day of Pentecost. Read Acts 2:36-40:
“Therefore let all Israel be assured of this: God has made this Jesus, whom you crucified, both Lord and Messiah.”We are in a pickle, if we are completely invested in believers baptism (only). Peter's words are, "be baptized, every one of you in the the name of Jesus Christ for the forgiveness of your sins. And you will receive the Holy Spirit. The promise is for you and your children...."
When the people heard this, they were cut to the heart and said to Peter and the other apostles, “Brothers, what shall we do?”
Peter replied, “Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins. And you will receive the gift of the Holy Spirit. The promise is for you and your children and for all who are far off—for all whom the Lord our God will call.”
With many other words he warned them; and he pleaded with them, “Save yourselves from this corrupt generation.” Those who accepted his message were baptized, and about three thousand were added to their number that day.
We take this text and impose our tradition on it, and cannot imagine that children could possibly be baptized. "Every one of you", means 'every one of you'. Children were present, families were present, on the day of Pentecost. 'The promise' is the gift of new life.
The question about baptism is, is it about God's grace or my faith? God's grace in Christ for me precedes my response. I can be baptized before I even have the ability to reason enough to believe, because baptism is about God's grace towards me, even before I make a decision.
I can also be baptized as an adult, when I believe (repent), and that is good too. In adult baptism, I am acknowledging what God has already done and affirming it. Do I need adult baptism, if I was baptized as a child? No. But, can I be baptized as an adult, if I was baptized as a child, but chose not to walk with God and only came to genuine salvation as an adult? Yes.
Baptism is open to all ages, because that is how it was done in the book. Baptism does not save you. Christ saves you and Christ does not save you through baptism either. Christ only saves people by what he did on the cross. Jesus' blood saves us. There will be no other boxes to check off.
Baptism is also immediate upon believing. It's, "let's find some water and do it". No waiting, no classes, no test, no confirming. All of that is baggage we have added- 'hamburger helper'.
Oikos: family and house
Oikos of God: family of God, house of God. the people are the family and the people are the house or temple. God is a family man. In the new covenant, the people are the temple that God comes to dwell in for service, Christ is the only sacrifice and we offer ourselves as sacrifices to God in Christ, and there is not special class of priests, but we are all now priest and Jesus is the only high priest.
No more going to the temple to find God, no more sacrificial rituals to please God, and no more priest-class that is a go between. In the oikos, we are all equal, we're all children, it's flat; there is no hierarchy. Every gift is for serving one another, like when many peolple bring different foods to a pot-luck buffet.
Thirty Years That Changed The World - The Book of Acts, Michale Green
Acts, F.F. Bruce