For historical interest’s sake:
“Before the Assembly convened, two prominent Westminster divines wrote important treatises on baptism, addressing the connection between baptism and regeneration in detail. Cornelius Burgess, in his Baptismall regeneration of elect infants (1629)…cites the Bible, the Fathers (Cyprian, Gregory of Nazianzus, Athanasius, Chrysostom, Jerome, Ambrose, Augustine), the Reformed confessions, and an array of Reformed theologians (Vermigli, Zanchius, Musculus, Junius, Bucer, Calvin, Pareus, Danaeus, Chamier) and English divines (Ames, Jewel, Whitaker, Fulke, Davenant, White, Featley, Hooker, Thomas Rogers, Thomas Taylor, and Aynsworth) in support of his view. He refers to the Second Helvetic Confession, the Scots Confession, the French Confession, the Belgic Confession, and the Heidelberg Catechism. Burgess’s argument is that regeneration is twofold. There is an infusion of grace by the Holy Spirit at the baptism of elect persons, including elect infants, while actual regeneration, which produces faith, occurs at effectual calling.
Daniel Featley, in A Second parallel with a writ of error served against the appealer (1626), is in broad agreement with Burgess, saying that ‘the inward grace ordinarily accompany the outward signe, and we ought to beleeve, by the judgement of Charity, that all who are baptised are truly regenerate.’ He also acknowledges, as Burgess does, that all who are baptized are not actually regenerate by the judgment of precise and infallible truth. ‘This is not alwaies,’ [always–CD] as the fathers speak, but those who are not elected. 
For both Burgess and Featley, all elect persons are regenerate in the initial sense at baptism and in the actual sense at effectual calling. On the other hand, nonelect persons are not regenerate in the initial sense at baptism, nor are they in the actual sense either. However, since we do not know who the elect are, we are by the judgment of charity to judge that all who are baptized are regenerate at baptism in the initial sense  (Robert Letham, The Westminster Assembly, pp. 333-334).
37. Daniel Featley, A Second parallel with a writ of error served against the appealer (London: Robert Milbourne, 1626) [STC 834.09], 90.
38. On the relationship between baptism and regeneration, see also Featley, The dippers dipt [Wing 2245:15]. Featley talks of baptism as the laver of regeneration (10-11), which was common currency in the debates at Westminster. See also Polyander et al., Synopsis purioris theologiae, 653.