Children and adults sin because we have a fallen nature, and it is God's grace that helps us avoid sin. We can't do anything without the grace God.
Children still disobey even when you tell them they will be grounded or punished by their parents. We are in a battle and we must pray for the grace of God, an extraordinary grace for our children these days.
I believe that a healthy fear of Hell is a good thing, but I believe that love of God is better.
If I want to instill guilt in my grandchildren for some evil habit, I tell them, think the next time you are tempted, it is as if you nail Our Lord to the Cross again, if you submit, because you know better, the other kids out there do not know what you know.
Not to say the teens are perfect but at least when they do something wrong they feel guilty, unlike many others.