Early teen makes more sense with your story so far, with the more advance vocabulary and moral expectations. I guess when I think "children's fable" I think younger kids like a 6-year old. A teen children's fable will be easier to make into a complex story that is also entertaining for the readers here though.
And I will, eventually. I love to concept and setup! My writing time is currently very limited, so I prioritize contest writing over It though.