Suggests baptism of all, including children.
Acts 2:38-39
Then Peter said unto them, "Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost. For the promise is unto you, and to your children, and to all that are afar off, even as many as the LORD our God shall call."

Acts 16:15
And when she was baptized, and her household, she besought us, saying, "If ye have judged me to be faithful to the Lord, come into my house, and abide there." And she constrained us.

Acts 16:33
And he took them the same hour of the night, and washed their stripes; and was baptized, he and all his, straightway.

Acts 18:8
And Crispus, the chief ruler of the synagogue, believed on the Lord with all his house; and many of the Corinthians hearing believed, and were baptized.

1 Corinthians 1:16
And I baptized also the household of Stephanas: besides, I know not whether I baptized any other.

Necessity of baptism for all, including children.
John 3:5
Jesus answered, "Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God."

Romans 6:4
Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.

"All have sinned" due to Adam's sin, including children.
Romans 3:23
For all have sinned, and come short of the glory of God;

Romans 5:12,19
Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned... For as by one man's disobedience many were made sinners, so by the obedience of one shall many be made righteous.

Psalm 51:5
Behold, I was shapen in iniquity; and in sin did my mother conceive me.

Circumcision (normally performed on infants cf. Genesis 17:12) replaced by baptism.
Colossians 2:11-12
In whom also ye are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ: Buried with him in baptism, wherein also ye are risen with him through the faith of the operation of God, who hath raised him from the dead.

Children can be believers.
Mark 9:42
And whosoever shall offend one of these little ones that believe in me, it is better for him that a millstone were hanged about his neck, and he were cast into the sea.

Luke 1:41-44
And it came to pass, that, when Elisabeth heard the salutation of Mary, the babe leaped in her womb; and Elisabeth was filled with the Holy Ghost: And she spake out with a loud voice, and said, "Blessed art thou among women, and blessed is the fruit of thy womb. And whence is this to me, that the mother of my Lord should come to me? For, lo, as soon as the voice of thy salutation sounded in mine ears, the babe leaped in my womb for joy."

Psalm 22:9-10
But thou art he that took me out of the womb: thou didst make me hope when I was upon my mother's breasts. I was cast upon thee from the womb: thou art my God from my mother's belly.