This story was very distinctive to me. The voice of the five-year old was striking in its maturity, but I noticed a gradual devlopment of the voice toward the end of the story when the reason he sounded so grown-up was made clear. I think that authors always have to be mindful of this when writing from the POV of a child, which is extremely difficult. But in this case it worked. I did notice but felt compelled to keep reading for answers rather than put the story aside out of inability to suspend disbelief.
Opening hooks? They make or break a story. When I'm reading for pleasure or as an editor, I know within 50 words if the author has enough skill to tell the story they're attempting. I won't keep reading if I have no confidence in the storyteller. "Reassigment" has a killer hook. It's not entirely unique in the world of fiction (think of The Lovely Bones and other books in a similar vein,) but it's plenty interesting and does its job well. In my opinion, no premise or storyline has to be 100% unique to be good. I mean, if you think about it--is there anything new under the sun? I believe it was King Solomon who said that centuries ago, yet we're still writing, reading, singing, and playing songs composed from the same 7-note scale.