There are hundreds of scripture that pertain to this. It is my belief that because of Adam we are all born with a sin nature. The infant you mentioned, Noone teaches an infant to throw fits, or to lie when they get caught doing something, it just comes natural. An infant learns that lieing is wrong, but he still doesn't understand the eternal consequences of sin until he much older. So, I agree with you that infants are not accountable, but I disagree because they do indeed sin from birth on, without even being taught to.
The wicked heart we are born with is the root of all of our sins. Focusing on the actual sin and not recognising the sin nature is like having an illness and treating the symtoms while letting the actual cause of the illness run amock.
So, yes, sin is imputed to us by Adam.
I am interested in what you think about Adam. Was he created with a pure heart (in God's own image), and did he choose to sin on his own?
Or was he created with a wicked heart as we are, and his sinning was just a matter of when, not if?
John