If, as you say, the sin of a child who is born sinless is from imperfection of the sins of the fathers causing mistakes and unwitting damage to the child
how did the fathers (and mothers, incidentally) become 'sinful'? You can run this cycle back and back as far as you want, but ultimately you have to be able to answer how that sin actually came to be present in what must, if your argument is correct have started out as a 'sinless' world.
You're not reading what JJ writes are you Andy? She mentioned a whole load of things that cause imperfection, only some of which are human-caused. She mentioned
famine, cold, fear of being killed by a wild animal, disease, tsunamis, terror, pain, toothache. How is it that you failed to spot what she wrote?