First, baptism is the time when one comes into contact with the blood of Christ, which washes away our sins and here they are to repent. How can a baby repent of something they have not ever done or even know what to repent of?

Acts 2:38
38 Then Peter said to them, “Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit.

Acts 22:16
And now why are you waiting? Arise and be baptized, and wash away your sins, calling on the name of the Lord.’

Secondly, children are of the kingdom and no one enters the kingdom, unless they are sinless.

Matthew 19:14
But Jesus said, “Let the little children come to Me, and do not forbid them; for of such is the kingdom of heaven.”


Thirdly, the are unable to obey Mark 16:16 to "believe".

And Forth, babies cannot "believe with all their heart" so they do not qualify or can they obey something un-obeyable (to make up a word). Notice Philip said, "if"...."he may"...

Acts 8:36-38
36 Now as they went down the road, they came to some water. And the eunuch said, “See, here is water. What hinders me from being baptized?”

37 Then Philip said, “If you believe with all your heart, you may.”
And he answered and said, “I believe that Jesus Christ is the Son of God.”[a]

38 So he commanded the chariot to stand still. And both Philip and the eunuch went down into the water, and he baptized him.