If you are saved, you are regenerated by virtue of the fact that the Holy Ghost is now in you.
Now the question is, when does man get the Spirit?
Ephesians 1:13 says, “In Him, Christ, you also after listening to the message of the truth, the gospel of your salvation, having also believed, you were sealed in Him with the Holy Spirit of promise.”
So you hear the message, you believe, you are sealed.
Also in Acts 10 Peter begins to declare the gospel Acts 10:34, “Opening his mouth Peter said…,” and it goes on to explain the gospel. Right in the middle of his speech, in fact, verse 44 says, “While Peter was still speaking these words, the Holy Spirit fell upon those who that were listening to the message.”
Would it be fair to assume that these poeple have just been regenerated? It says that all the circumcised believers who had come with Peter were amazed because the gift of the Holy Spirit had been poured out upon the Gentiles also. They were saved, regenerated.
Check out the next verse, verse 46, “For they hearing them speak with tongues and exalting God. ‘Surely no one can refuse the water for these to be baptized who have received the Holy Spirit just as we did.’” Here’s where the water comes in. It’s coming in after regeneration. After they have certainty that they belong to God because now they are in the Spirit.
After they have been regenerated. After they have Jesus inside of them, having been cleansed by faith. After they have the knowledge that they have eternal life, according to John in 1 John 5. Now water comes into play. To me, this is a very profound biblical proof that water is not necessary for salvation.
When people become Christian, they get baptized as they ought because Jesus commanded it. But they get baptized because they’ve been saved, regenerated, not in order to get saved.
To come back to your question, the Holy Ghost washes over the new believer, He regenerates him at the moment of newfound belief. Since infants and newborns cannot have that newfound belief yet, they recieve the Holy Ghost upon confirmation.
I hope I was clear enough in my explanation, you see, english is not my first language. And sometimes I have to muddle through. I apologized in advance for my murky explanation.
God Bless !