Scripture speaks of the doctrine of baptisms, plural. One of those baptisms is by immersion into water, following one’s profession of faith in Jesus Christ. First believe and then be baptized in water is the sacred order. It’s important to realize that baptism, in and of itself, doesn’t save us.
The 3,000 on Pentecost repented and were saved before they were water baptized, as was the case of Cornelius’ household. In baptism, there is the symbolizing of death to the old life of sin and a resurrection into a new life in Jesus Christ. Thus, infant baptism is not the time of a person’s new birth, as some believe, because there can be no repentance or sense of need on the part of the infant for the saving grace of Jesus Christ.
Yes, there is to be a childlike demeanor when we enter the kingdom of God, but we do not enter the kingdom of God as infants biologically. As heart circumcision proved physical circumcision to be valid, so does the regenerating work of God’s Holy Spirit make the act of water baptism valid.
Believe and be baptized, then teach this pattern wherever you go.