I assume that Reformed people other than Reformed Baptists (e.g. Christian Reformed, Presbyterian, Congregationalist, etc.; those in the Calvinist/Geneva tradition) follow John Calvin on the issue. He taught that there is no danger to the child of Christians if baptism is withheld; they are still within God's covenant promise. Calvin was no baptismal regenerationist, and in response to their teaching, he says,
We nowhere read of [Christ] having condemned him who was not yet baptised.... By assenting to their fiction, we should condemn all, without exception, whom any accident may have prevented from procuring baptism.... Let them now consider what kind of agreement they have with the words of Christ, who says, that “of such is the kingdom of heaven” (Mt. 19:14). (Calvin, Institutes IV.16.26.)
Baptism is the sign of regeneration, but not itself the
means of regeneration, which is the Holy Spirit:
Therefore, as to baptise with the Holy Spirit, and with fire, is to confer the Holy Spirit, who, in regeneration, has the office and nature of fire, so to be born again of water, and of the Spirit, is nothing else than to receive that power of the Spirit, which has the same effect on the soul that water has on the body. (Institutes IV.16.25).
Rather, the sin is in withholding baptism to infants: "it is not less applicable to children than to those of more advanced years, and that, therefore, they cannot be deprived of it without manifest fraud to the will of its divine Author" (
Institutes IV.16.8).