[xzins]

Matthew 21 15But when the chief priests and the teachers of the law saw the wonderful things he did and the children shouting in the temple area, "Hosanna to the Son of David," they were indignant. 16"Do you hear what these children are saying?" they asked him. "Yes," replied Jesus, "have you never read, " 'From the lips of children and infants you have ordained praise'[1] ?"

Jesus declares infants to be innocent.

How do we reconcile this with "All have sinned and fall short of the glory of God?"

One is not culpable until one sins. Therefore, the all refers to "all of a culpable age."

[OrthodoxPresbyterian]

Jesus declares infants to be innocent.

No, he does not.

Jesus says of a specific group of children who are brought to Him, "the kingdom of heaven belongs to such as these".

There is not a single verse of Scripture anywhere in the Gospels where Jesus states, "infants are Innocent of Sin".

This is what you need Jesus to say.
This is what Jesus does not say.

If you have a specific verse where Jesus specifically states, "infants are Innocent of Sin", present it.

Because Matthew 19:13-14 does not say "infants are Innocent of Sin". Those words are NOWHERE in the passage!! It says, "some children were brought to Him... the kingdom of heaven belongs to such as these", a statement which is Calvinist to the core.

How do we reconcile this with "All have sinned and fall short of the glory of God?" One is not culpable until one sins. Therefore, the all refers to "all of a culpable age."

Nope. Paul begins his discussion with a reference to the infant rite of circumcision:

What advantage then hath the Jew? or what profit is there of circumcision? (Romans 3:1)

If "all" meant "all except those of a young age", then prefacing the discussion with a reference to the infant rite of circumcision woul have been nonsensical.

All have sinned.

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: (Romans 5:12)

Death passed upon all men, for that all have sinned. The fact that all are born mortal, is juridically founded upon the fact that all have sinned.
If Infants have not Sinned, they would not be born mortal. If the were not sinners, they could not die in infancy. Death passed upon all men, for that all have sinned.