Peace,
Original sin is the inherited tendency to sin.
That's all it is.
All of us are born with this inherited tendancy to sin, otherwise we would all be perfect.
It's really not a difficult concept.
"Islam teaches us that every child is born Muslim"
In Christianity NO ONE is born a Christian.
One becomes a Christian by himself, it must be of his choice.
We also believe that little children are innocent and will never be damned if they unfortunately die young.
Blessings