It took me a little bit to understand this, but now I think I do. What you're saying is that I need to understand my reader and how they think and what they expect. And I'm just throwing this out here, but what if I got a middle grader to read my one of my short stories? My little sister is in the range I'm aiming for, so what if I gave/paid her to read it? Then I could see if kids would get and enjoy the adult's POV. I know that's only one reader, but it might help, along with your suggestion to read some more upper MG.
Thanks.
Sorry if I wasn't clear, but no, having a kid read your stuff (especially a family member or friend) isn't going to do what I suggested.
Imagine you love mysteries, and someone told you they'd written a mystery. You ask what kind it is, like a cozy or hardboiled, and they say they dunno, they read a few a decade or two ago, but it's a mystery! You would probably not have confidence it's something you're interested in reading, if the person who wrote it doesn't read mysteries, and thus doesn't know the types, or how most mysteries are set up, how they're paced, what mystery readers like about mysteries.
Would you watch a sci-fi movie made by someone who had never really watched or read sci-fi? Think of the mistakes they could make if they didn't know stuff like Asimov's rules for robots existed, or if they'd never seen the depictions of aliens, and they just had a sci-fi movie about an alien named Bob, who looked just like humans, and flew to Earth on a plane from Mars. This would not be a successful movie, because it wouldn't make sense to sci-fi watchers and readers. It's not that every robot has to hone to the rules, or that every alien has to be a grey or whatever, but there should be a reason they're not what people expect, and to do that, the writer has to be really, really aware of what people do expect.
You can't break the rules until you KNOW the rules.
This goes for most things in life. If you bake, and you know, say, the basic ratio for muffins, and how adding extra butter makes a cookie behave vs. extra sugar vs. molasses vs. etc. -- if you know you can add alcohol and it won't have the same effect as milk or water-based things, then you can fuck around with recipes, make up your own recipes, etc., because you understand the rules of baking. If you haven't spent tons of time baking, to where you understand all those rules and more, and you wake up one day and decide to make cookies, and think you love butter cookies, so you're going to make shortbread but just add extra butter because you love that buttery taste, you're not going to end up with cookies. You're going to end up with a mess unrecognizable to people who like cookies. Asking someone who likes cookies to taste it after the fact won't change anything.