I have found the perfect material to use with this adventure as well as a good recommendation for other Grimm players, that is from the Puppetland RPG that used to be released by Hogshead Publishing years ago.
The setting of Puppetland is that there was once a human puppet maker who created Puppetland, but one day Punch turned bad and killed him and then skinned him, using his skin to create six evil puppets.
So the children will have to find and destroy each of the evil puppets and then collect the skins to hopefully revive the maker, with the help of the maker's tear stored inside a thimble carried by the puppet Judy. Eventually they will have to face punch and defeat his sadistic kingdom before the kids can finally leave the Grimm Lands and head to the North Pole to meet Santa.
The puppet maker is perfect in line for the Christmas adventure since it'll involve toys.
But check out the Puppetland RPG, it has a good background to use with Grimm.