To sin is to KNOW you're doing wrong. Babies don't know. You're twisting the Scripture.
You hit the point of the matter that Scripture teaches: sin is not some nature in our skin and bones we are born with, nor some spirit in the air breathe into our lungs, but is a deed and act in word or tongue. Sin and righteousness are spiritual
in nature, in that they begin within the heart, whether to desire to
do thy will O God, or to lust for sinning against Him, even as Lucifer first did:
How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations!
For thou hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north.
Thou wast perfect in thy ways from the day that thou wast created, till iniquity was found in thee.
Whether angels or men, sinning is a conscience act on our part beginning spiritually in the heart. The only difference between angels and men, is that men are created a little lower than the angels, as babes born with mortal bodies.
Both angels and men are created alive and clean of conscience by Christ, and also with power to choose good or evil. Angels are created without age nor childhood like men, where their is a pure time of no conscious thinking. This is why babes and cubs act the same by nature, neither sinful nor righteous, just babes and cubs.
The problem with humanist thinking applied to the things of God, is they begin to define what is sin and righteousness, rather than letting God do so. They say the 'sin nature' is shown by letting two toddlers into the same playpen with toys. The thing of course is that competition is not a sin. Now if one of those toddlers started cursing out the other, then of course we hear sinning itself.
But of course, as you say, babies neither know nor speak, whether sinfully nor righteously.