This book is marketed to middle grade children. A novel from a doll's viewpoint may sound very sweet and whimsical, but parents need to be aware that the doll's experiences in both the Land of the Dolls and Poland deal with mature themes. Your child may be ready to learn about invasions and genocide, or may have already been exposed to these themes in another context. Yet I would still recommend that parents read this book with their children and discuss it with them.
As an adult reader, I found the book rewarding. I could draw parallels between the way dolls were viewed by invaders in the Land of the Dolls, and the treatment of androids on the first season of the television series Humans (for more information see the article about this science fiction series on Wikipedia ) which is also similar to the stigmatization of Jews and other minorities as sub-human by some members of dominant groups throughout history.
Another aspect of this book that fascinated me was the Eastern European folklore. R. M. Romero dropped figures from local myths and legends into 20th century Poland. As a Robin Hood fan, I particularly enjoyed the presence of Juraj Jánošík, who was a Robin Hood figure. His legend was based on an actual highwayman who lived from 1688-1713 according to his article on Wikipedia . I also found a blog entry about him dealing more extensively with the legend at "Robbing The Rich: Juraj Janosik" . He was supposed to have been given three magical objects by mythic figures who may have been either goddesses or witches.
From the author's note I learned that this novel took its current shape due to Romero's visits to the site of the concentration camp at Auschwitz in 2005 and 2016. These experiences and her associated research lend the book its historical authenticity. Its magical and mythic elements make The Dollmaker of Krakow an outstanding fantasy novel.