In a grim militaristic society, any child that shows a spark of creativity is labeled an Unwanted and is taken away to be put to death.
Called "The Hunger Games meets Harry Potter" by Kirkus Reviews, author Lisa McMann (The WAKE series) writes her first middle-grade fantasy, and it is a winner.
Separated from his twin during the purge, Alex (an Unwanted) discovers an enchanted land where creativity equals magic. This hidden land must eventually go to battle with the military of his former world, and both worlds must change to survive.
4 Elves - highly recommended