In Psalm 51:5, when David said he was shaped in iniquity and conceived in sin, what did he mean? We know that his parents were married when he was conceived, therefore the circumstance of his conception was not in sin. Rather, David his saying that from the moment he was conceived, he was a sinner. That an unborn child who has never committed any acts of sin is generally hard for most people to believe. But David did not say he had personally committed any acts of sin but that he was a sinner.
Ro 5:12 Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:
Sin entered the world when Adam ate the forbidden fruit. God told Adam “…. of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.” Ge 2:17
Not only did Adam die but his death passed upon all men. And the reason all men die is because we all have sinned. Romans Ro 5:19 concludes, For as by one man’s disobedience many were made sinners, so by the obedience of one shall many be made righteous.
There you have it. By one man’s disobedience many (in this case everyone who is a descendant of Adam, which excludes no one), in other words everyone, became a sinner. Even infants die. Romans 5:12 tells us the reason is because they are sinners not necessarily by action but by nature. When the scripture says, “for all have sinned,” it means we sinned in Adam or were in Adam when he sinned and are therefore sinners. The sin nature is passed down from generation to generation, all the way from Adam to this present generation. Only Jesus Christ can change a person’s sin nature through the new birth of the Holy Spirit.
Because children are born with a sin nature it doesn’t take long for that nature to be made manifest. Psalm 58:3 states, The wicked are estranged from the womb: they go astray as soon as they be born, speaking lies. The estrangement is not from their parents but from God. And it is because of every person’s estrangement from God that “the wicked” which includes all unbelievers, including unregenerate children, need corrective behavior. It doesn’t take long for an infant to begin speaking lies.
Lies and sins in general are based on our natural self-centeredness. This self-centeredness is part of man’s fallen sin nature inherited from Adam. It is part of the parents job to teach their children that this is sin and will not be tolerated.