I hope you realize that the doctrine of original sin is
theologically ambiguous. In fact, noted Christian apologist William
Lane Craig believes that when infants or small children die, they
go to heaven. He uses it to justify the God-sanctioned genocide of
the Canaanites.
But if you truly believe in Original Sin, you have to explain
whether it is fair and just that someone who has never heard of
Christianity is condemned to eternal hell for not believing in
Jesus.
I also think the parent-child analogy is fraught with flaws. Go
ask any parent if they would be willing to condemn their children
to eternal punishment for one bad decision. Maybe a parent will
accept a life in prisonment, or even the forfeiture of life itself,
for a grievous crime commited by the child. But eternal hell just
because, say, your child chose Buddhism (and a life of kindness)?
Come on.
The doctrine of original sin is NOT theologically ambiguous. In
fact, even an atheist like Richard Bozarth is clear about what it
is! He wrote, "Christianity has fought, still fights, and will
continue to fight science to the desperate end over evolution,
because evolution destroys utterly and finally the very reason
Jesus’ earthly life was supposedly made necessary.
Destroy Adam and
Eve and the original sin, and in the rubble you
will find the sorry remains of the Son of God. If Jesus was not the
redeemer who died for our sins, and this is what evolution means,
then Christianity is nothing."
See also http://creation.com/alexander-original-sin
It is misleading to claim that William Lane
Craig justified the "genocide" of the Canaanites with the
reason that infants go to heaven when they die. He did not do this.
In fact, he justified it by saying that God sanctioned a total
extermination of the Canaanites by the Israelites because of their
depravity. Here you have 400 years of Canaanite children being born
and brought up just as sinful as their fathers, something the
Bible critic overlooks. And for those Bible critics who are
"genuinely" concerned for these infants and young children,
Christian apologists reply that they will go to heaven to be with
God.
Lastly, to your charge that original sin is unfair, see a
response here http://creation.com/original-sin-at-the-bbc