But doesn't it presume to know that God creates innocent babies - born and forever - reprobate?
No, the confession gives us no idea since it is impossible to know the mind of God.
VI. As God has appointed the elect unto glory, so has He, by the eternal and most free purpose of His will, foreordained all the means thereunto. Wherefore, they who are elected, being fallen in Adam, are redeemed by Christ, are effectually called unto faith in Christ by His Spirit working in due season, are justified, adopted, sanctified, and kept by His power, through faith, unto salvation. Neither are any other redeemed by Christ, effectually called, justified, adopted, sanctified, and saved, but the elect only.
VII. The rest of mankind God was pleased, according to the unsearchable counsel of His own will, whereby He extends or withholds mercy, as He pleases, for the glory of His sovereign power over His creatures, to pass by; and to ordain them to dishonor and wrath for their sin, to the praised of His glorious justice.
VIII. The doctrine of this high mystery of predestination is to be handled with special prudence and care, that men, attending the will of God revealed in His Word, and yielding obedience thereunto, may, from the certainty of their effectual vocation, be assured of their eternal election. So shall this doctrine afford matter of praise, reverence, and admiration of God; and of humility, diligence, and abundant consolation to all that sincerely obey the Gospel. - Westminster Confession-Effective Calling
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EFFECTUAL CALLING
III. Elect infants, dying in infancy, are regenerated, and saved by Christ, through the Spirit, who works when, and where, and how He pleases: so also are all other elect persons who are incapable of being outwardly called by the ministry of the Word.
IV. Others, not elected, although they may be called by the ministry of the Word, and may have some common operations of the Spirit, yet they never truly come unto Christ, and therefore cannot be saved: much less can men, not professing the Christian religion, be saved in any other way whatsoever, be they never so diligent to frame their lives according to the light of nature, and the laws of that religion they do profess. And to assert and maintain that they may, is very pernicious, and to be detested.