"They (Adam & Eve) being the root of mankind, the guilt of this sin was imputed, and the same death in sin and corrupted nature conveyed to all their posterity, descending from them by original generation" [emphasis added] (The Westminster Confession of Faith; VI/3).
What do you think that the word "conveyed" means? How is that different from the word "imputed"?
Besides that, the Calvinists teach that "the guilt" of Adam's sin is imputed to mankind. If the Calvinist are right then the sin of Adam was imputed to his sons, Cain and Abel. However, what is said here contradicts that idea:
"The soul who sins is the one who will die. The son will not share the guilt of the father, nor will the father share the guilt of the son" (Ezek.18:20).
What is said here declares in no uncertain terms that children do not bear the guilt of the sins of their father.