The poster has answered, they as well as I have stated that babies sinned in their federal head Adam, this belief is derived from Rom 5:12Please read my post again as you must have overlooked the scripture I gave.
BTW, you have never answered our question in telling us exactly how does a baby sin and please do not use those scriptures you have already given that only Calvinist like to use to prove their point as a few of us have told you they do not cause a baby to sin. If you keep up this line of babies sin then this would have made Jesus a sinner at His birth.
12 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:
Now if you or anyone else doesn't agree with that, fine, you may see it differently, but acknowledge that the poster attempted to answer your question, you just dont agree, which is fine.