... babies are born innocent and are not depraved therefor born sheep, it
is then after they lose innocence by sin that they become goats or lost sheep
In Adam all died, babies included. They are conceived in sin, and come forth out of the womb, speaking lies. No one is innocent, no one is righteous, save one: Christ Jesus.
The sheep are those depraved sinners on whom God has mercy. They were lost sheep before he called them and drew them to himself.
As the popular song goes, I once was lost but now am found, was blind but now I see.
P.S. Of course, the metaphor of "sheep" can be used other ways, such as to contrast with goats, or to represent a relationship other than a saving relationship (such as a king being the shepherd and the citizens of his nation, the sheep).