Augustine's original sin idea brought forth the catholic sacrament of baptizing infants, as if that would save them from original sin. I believe we all are born with a sinful nature, inherited from Adam and Eve, and that we do sin because of it. Children (of such is made the kingdom of Heaven), have an age of accountability, when they can understand the gospel and be saved. I did so at age 8. Moved to another town, and at 14, I told the church I believed and even prayed the prayer I prayed at the age of 8, accepting Christ into my heart, and was baptized as a believer as an outward profession of my faith, symbolizing that I was dead in Christ, buried with him in baptism, and ressurected a new creation in him. I have been growing ever since, and now I am 40.
As for sin, if you believe in the Bible, you must surely believe in sin. If you do not believe the Bible then you may have your own opinions. According to the Bible, God is Holy, Just, Pure, Good, Light, a consuming fire, and many other things. Sin cannot be in his presence, the sinner would be consumed. He gave the commandments, written in our hearts, to show us our sin, and he that breaks one point of the law is guilty of all. Example, if u ever told a lie, u r a liar, if u ever stole, u r a thief, lusted after a woman/man? an adulterer, ever used the Lord's name in vain, a blasphemer, hated a brother without cause, a murderer according to I John, so right there, this person is a lying, thieving, adultering, blaspheming, murderer at heart, and is doomed on judgement day when he stands before Almighty God.
But that doesn't have to be now does it? Christ paid for all the sins of all the world with one sacrifice and offers salvation as a free gift, to any who will believe that he did so, and trust in his death alone to pay for their sins. So he is our cloak of righteousness, our advocate, our mediator, our saviour. He has already paid the price for all to be saved, and rose again giving us power over sin, and gave us the Holy Spirit to lead us and show us where we need to change to grow in his grace, secure in his hand. Some folks listen and work and grow more than others, and others do not, but each will have his reward, some folks saved and not much to show, others with great reward. But one day, this mortal shall put on immortality, this corruption shall put on incorruption, and we will sin no more, Praise God, Halleluia! PEACE!