About 10 years ago, I had a wonderful Sunday school class of 4-6 year old children. They listened well, and made it a joy to teach. One Sunday, as I was teaching a Bible story, the subject of sin came up. I asked if anyone could tell me what "sin" was.
Five-year old Natalie knew exactly what sin was:
"It's when a man and a woman live together who aren't married, or when two women live together."
"Umm, yes, that's an example of sin."
Hopefully, the other children did not go home and tell all that they learned in Sunday school, or have any interesting questions for their parents! Natalie was taught that day that sin was something she did too (and every single person on earth) and it included things such as lying, being mean to siblings, and disobeying parents!