If you are hoping for the child reader to discover and grasp the message on their own that would require them being able to read.
My seven year old just this school year has not only learned to read but has become a varacious reader (which I love!) but ideally I would think being able to reach younger children through their parents reading the story as well as being able to reach that young reader... and even the parents themselves would be the ultimate goal.
What a great topic of discussion ... how do we hit everyone in some way, even while we are focusing more on one particular age group?
I know I'm rambling... hopefully some of it makes sense