John Calvin taught baptismal regeneration as the following quote shows:
“So then we must ever come to this point, that the Sacraments are effectual and that they are not trifling signs that vanish away in the air, but that the truth is always matched with them, because God who is faithful shows that he has not ordained anything in vain. And that is the reason why in Baptism we truly receive the forgiveness of sins, we are washed and cleansed with the blood of our Lord Jesus Christ, we are renewed by the operation of his Holy Spirit.
And how so? Does a little water have such power when it is cast upon the head of a child? No. But because it is the will of our Lord Jesus Christ that the water should be a visible sign of his blood and of the Holy Spirit. Therefore baptism has that power and whatsoever is there set forth to the eye is forthwith accomplished in very deed.”
[John Calvin, Sermons on Deuteronomy, p. 1244.]