Baptism is the sign and seal of being born into the Body of Jesus Christ. As a sign, it points to something else beyond the water — new life from God. As a seal, it is a sacrament commanded by our Lord Jesus.
In the Presbyterian church, infants and children may be baptized, or a person may choose to be baptized for the first time as an adult. The New Testament reports predominantly adult baptisms, but does indicate that families also received the sacrament, e.g., the Philippian jailer and family in Acts 16. In Peter’s Pentecost sermon, he indicated that the new covenant “is for you and your children.”
Baptism always happens during a full Sunday worship service, because it involves the whole covenant community. An ordained minister of the church places water on the person’s head and baptizes him or her, “In the name of the Father, the Son, and the Holy Spirit.”