There are some Christians who believe Adam committed the first sin, which led everyone to sin after the removal from Eden. They believe that from the moment of birth, each individual becomes a sinner.
Despite the sincere beliefs held by those Christians, there is no Biblical evidence to support the claim.
Adam and Eve were innocent until the fruit from the tree of knowledge of good and evil was eaten. Prior to that moment, they had the innocence of children. Without knowing what good and evil is, one cannot choose to sin. Having that knowledge is necessary to commit acts of good and evil.
Knowledge and understanding are required by God, which is the reason sin is never mentioned about Adam or Eve, even after they ate the fruit. It is not until Cain that sin is mentioned the first time.
“Then the Lord said to Cain, “Why are you angry? Why is your face downcast? 7 If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must rule over it.”
Prior to that moment, sin does not appear anywhere in Genesis. Had Adam or Eve sinned, the Bible would have made that every bit as clear as with Cain. Without God calling them sinners, it makes it clear neither committed any actual sin.
There is no one sin God sees as worse than others. To God, sin is sin without distinction, and each individual is responsible for their own sins and seeking forgiveness.
“The one who sins is the one who will die. The child will not share the guilt of the parent, nor will the parent share the guilt of the child. The righteousness of the righteous will be credited to them, and the wickedness of the wicked will be charged against them.”
The wording makes clear there is no singular sin that follows from one generation to the next. Each is responsible only for their own sins. No one can sin for another person, since each has free will to follow God or man.
There is no original sin. There is just sin.