If we are not born with a sin nature then why does every child have to be taught not to sin even before they ever know sin? No one ever has to teach a child to be a liar as they are all born liars. No child learns to lie. It comes naturally. No child learns to be selfish it comes naturally. No child needs to learn disrespect, it comes naturally. Yes we have a sin nature at birth. Even a month old baby knows how to gets its way by crying even when there is no pain.
Children are born with a temptation nature. When they see something, they WANT it. We have to teach a child not to take every cookie on the plate and share with his family.
The scriptures say our flesh LUSTS against our spirit. It does not make us sin, but it tempts us to sin. When we get angry, the flesh wants to strike another person, or even kill a person. But we do not have to obey our fleshly desires. When we see something we like, the flesh wants to steal it. But we do not have to obey and steal.
Let me ask you a question, is a person born a drug addict? NO. A person first begins to take drugs, and then becomes addicted. Smoking is the same, no one is born with a cigarette in their mouth. The first time to try to smoke you will cough and choke. But it you continue to smoke you will become addicted and it will be your "nature" to smoke. This applies to many things, we all hunger. Hunger is not wrong, but if we do not control it we can become addicted to eating and become obese. This can create real health problems.
The scriptures say God cannot be tempted with evil.
James 1:13 Let no man say when he is tempted, I am tempted of God:
for God cannot be tempted with evil, neither tempteth he any man:
But Jesus could be tempted. He inherited this "temptation nature" from his mother Mary through her flesh.
Heb 4:15 For we have not an high priest which cannot be touched with the feeling of our infirmities;
but was in all points tempted like as we are, yet without sin.
Jesus felt temptation. After he fasted for 40 days he was very hungry. He wanted to eat just like we do, and this is why the devil tempted Jesus to turn stones to bread.
Luke 4:1 And Jesus being full of the Holy Ghost returned from Jordan, and was led by the Spirit into the wilderness,
2 Being forty days tempted of the devil. And in those days he did eat nothing: and when they were ended,
he afterward hungered.
3 And the devil said unto him, If thou be the Son of God, command this stone that it be made bread.
The devil knew Jesus felt temptation, that is why he tempted Jesus to turn the stones to bread. He was trying to attack Jesus's weakness. But Jesus did not obey this temptation and did not sin.
This temptation nature was before the fall. Eve was tempted by the tree of knowledge of good and evil.
Gen 3:6 And when the woman saw that the tree was good for food, and that it was pleasant to the eyes, and a tree to be desired to make one wise, she took of the fruit thereof, and did eat, and gave also unto her husband with her; and he did eat.
Adam and Eve were made flesh. They had lusts and desires. It is these lusts and desires that Satan attacked. He told Eve she would be like God, this appeals to the pride. The tree looked good to eat, this appeals to the appetite.
The problem is people cannot distinguish between temptation and sin. Eve was tempted by the fruit on the tree of knowledge of good and evil, but if she would have resisted and walked away, she would not have sinned. It is when she obeyed these lusts in opposition to God's command that she sinned.