Herman Bavinck, Reformed Dogmatics Volume 4, p. 56
“Reformed theologians unanimously agreed on the following points:
That the benefits of the covenant of grace were usually distributed by God in connection with the means of grace; hence regeneration is in connection with the Word;
That God, however, is not bound to these means, and hence he could also take an unusual route and regenerate and save especially young children without the Word;
That he, as a rule, worked that way in the case of children of believers who were taken by death before reaching the age of discretion;
That the baptized children of believers who were part of the life of the congregation had to be considered elect and regenerate until the contrary was evident from what they said and did; and
That this however, was a judgment of charity, which must indeed be the rule for our attitude toward these children but cannot claim to be infallible.
On the other hand, from the very beginning there was disagreement over whether the children of believers, to the extent that they were elect, were regenerated already before, or in, or only after baptism. Some—like Martyr, a Lasco, Dathenus, Alting, Witsius, Voetius, Mastricht—tended to favor the first view. But the majority—Calvin, Beza, Musculus, Ursinus, de Bres, Acronius, Cloppenburg, Walaeus, Maccovius, Bucanus, Turretin, Heidegger, and others—left the question undecided.”