Just re-read the OP and I see better what you're driving at. Well done.
I think that any group of reasonably bright, non-indoctrinated kids would find the story of Jesus to be fiction (and more than a little scary). Taking that as a model, I might want the kids to think about the following.
1. Do the characters in the stories do things that, as far as you know, people can't do?
2. Does nature behave in the story differently from how you've seen nature behave in your own life?
3. Is there anything about the story that seems impossible to you?
If you answered 'yes' to any of these questions, then the story is probably fiction.
Boru
I think that any group of reasonably bright, non-indoctrinated kids would find the story of Jesus to be fiction (and more than a little scary). Taking that as a model, I might want the kids to think about the following.
1. Do the characters in the stories do things that, as far as you know, people can't do?
2. Does nature behave in the story differently from how you've seen nature behave in your own life?
3. Is there anything about the story that seems impossible to you?
If you answered 'yes' to any of these questions, then the story is probably fiction.
Boru
‘I can’t be having with this.’ - Esmeralda Weatherwax