Baptism is the vehicle through which God washes our sins away by water

FH:How is an infant changed? Please, enlighten us all....

It is the work of God. There are somethings which are God's domain. Do you claim to know how Jesus raised men from the dead and healed people of illness. If you can explain that mystery, then you already know how God changes the infant in Baptism.

Seems you forget that the change comes PRIOR to baptism....

No. It is you who forget that God takes into account the faith of the parent. Let me show you:

Here, Jesus healed one based upon his own personal faith:
Luke 18:42
And Jesus said unto him, Receive thy sight: thy faith hath saved thee.

Here, we see Jesus healing someone based upon the faith of their loved ones, be they friends or family:
Matthew 9
King James Version (KJV)
1 And he entered into a ship, and passed over, and came into his own city. 2 And, behold, they brought to him a man sick of the palsy, lying on a bed: and Jesus seeing their faith said unto the sick of the palsy; Son, be of good cheer; thy sins be forgiven thee. 3 And, behold, certain of the scribes said within themselves, This man blasphemeth. 4 And Jesus knowing their thoughts said, Wherefore think ye evil in your hearts? 5 For whether is easier, to say, Thy sins be forgiven thee; or to say, Arise, and walk? 6 But that ye may know that the Son of man hath power on earth to forgive sins, (then saith he to the sick of the palsy,) Arise, take up thy bed, and go unto thine house. 7 And he arose, and departed to his house.

I love that verse because it shows that Jesus washes away sins based upon the faith of one's loved ones and friends.

And here, we see that Jesus healed the woman's daughter based upon the mother's faith, not upon the daughter's. 
Matthew 15:21-28
King James Version (KJV)
21 Then Jesus went thence, and departed into the coasts of Tyre and Sidon.


22 And, behold, a woman of Canaan came out of the same coasts, and cried unto him, saying, Have mercy on me, O Lord, thou son of David; my daughter is grievously vexed with a devil.


23 But he answered her not a word. And his disciples came and besought him, saying, Send her away; for she crieth after us.


24 But he answered and said, I am not sent but unto the lost sheep of the house of Israel.


25 Then came she and worshipped him, saying, Lord, help me.


26 But he answered and said, It is not meet to take the children's bread, and to cast it to dogs.


27 And she said, Truth, Lord: yet the dogs eat of the crumbs which fall from their masters' table.


28 Then Jesus answered and said unto her, O woman, great is thy faith: be it unto thee even as thou wilt. And her daughter was made whole from that very hour.

baptism is a sign of what God has already done, which is made us new creations in Christ.

Baptism is the vehicle through which God washes our sins away by water. Just as He washed away the illness of Naaman:
2 Kings 5:14

King James Version (KJV)
¹⁴ Then went he down, and dipped himself seven times in Jordan, according to the saying of the man of God: and his flesh came again like unto the flesh of a little child, and he was clean.

Sincerely,

De Maria