Short Stories: one leads to a Mid-Grade book

I have recently written the text to 5 Children’s Picture Books (artwork needs to be done by someone who can draw…I can’t).  Anyway, upon hearing this, my 12 year old grandson asked me to write a story with him as the central character.  I immediately went home and wrote, “Fetch,” a short story wherein my grandson is a wizard, but is unaware of it, but discovers it as the story unfolds.  I like the story so much that I intend to turn it into a Mid-Grade book.  Thanks, Darren for the inspiration!