A little more gelling. I'm looking at what was going on in 19th century Germany -- the emancipation of Jews there, along with a growning anti-semitic backlash. I'm seeing Clara as belonging to a prosperous assimilated Jewish family who celebrates Christmas as many assimilated Jews did in 19th century Germany. (Note: along with America, Germany was seen by 19th century Jews as an enlightened nation to escape to when fleeing Russia and the Ukraine.)
I'm seeing a three sided battle: the spirit of the enlightment - represented by emancipation and sanitary reform -- modern drains that will help prevent disease, but also assimilationism and rejection of much of Jewish spirtuality and culture. A second side of the battle is the spirit of reaction - opposing the drainage, opposing emancipation, and also linked to even darker forces - the Rat King - with hopes of reviving the 14th century plague, blaming the Jews and importing Pograms from Russia and the Ukraine. A third force is the spirit of old "Yiddeshe" Judiaism that the assimilationist reject - the only spiritual force strong enough to oppose the rat king. It takes the form of a toy soldier made of clay - a golem of sorts. It is only when the new enlightment and the best of Jewish tradition come together (in the alliance of Clara and the clay soldier) that the dark forces can be defeated - at least for the moment. The sugar plum fairies, and tea fairies and Ginger snap fairies and what have you are ghosts raised by the Rat King (I really think turning him from a mouse king to a rat king works well.) I suspect they can be turned against him, since they are his past victims. I don't really have a plot yet, or real characters, but I think this is the beginning of real world building. Given a world and peoples places in it characters I hope will follow naturally. Given a world, and the people who live there, I hope they will follow their natural inclinations and provide a plot.
t Update
And now I'm suddenly deciding - it is not a clay toy, but a full size golem. Originally her father does bring home a nutcracker. Older jealous brother breaks it, and Father to make it up to her drags down the old clay man that is up in the attic. Has been in the family for generations, since before they emigrated to Germany from Prague. Has all sorts of dark superstitious attached to it. It will serve much better as a child's toy than as a magnet for superstitious nonsense. And now I know his character. So little Clara has a full sized clay man as her new toy - with letters carved on his forehead. Some of the letters have been rubbed out, but her Grandpapa taught her a few Hebrew letters behind her father's back so she could play the dreidel games. So she can see what the letters should be, and uses her finger to make them clear where they have blurred.