I read a fascinating account of a mother whose ten year old daughter asked her, "Mom, what is sin?" Theater performers had used to word in front of them and the child had been raised without religion. She did not recall hearing the word before.
There must be today thousands of U.S. children being raised in homes where the word sin never comes up. Their social circles are with people who do not use the word. Most everyone reading this and myself grew up hearing the word daily. How would our lives be different if we, like the ten year old above, had never heard the word.
Here is my take on how the word is used. To the groups I call fundamentalists or evangelicals, the word is used to threaten children. The mother above said she was told constantly as a child sin led to punishment from God including hell.
If this is the only childhood circumstance you have ever known, you might wonder how children learn right from wrong? For that matter, how do the children's parents know right from wrong?
If it were possible to investigate this, I'm confident we would find children of parents who never introduce or teach their children about sin know right from wrong as well as those of religious parents. We know from law enforcement records that nonbelievers are under represented in jails and prisons. If atheists had no way to determine right from wrong, if they lived lives of "anything goes", they would be in prison more than Christians. But, the opposite is true.
Parents who are not believers, I would propose, look around them and figure out what rules people have to follow for society to be successful. They teach their children what they themselves have figured out.
Children do not need to know the definition of "sin" to grow up and become successful adults.