Katherine Rundell's Rooftoppers (2013) is charming to the point of Disneyfication, a collection of adorable figures and improbable coincidences that would be utterly saccharine if it didn't work so damn well.
Sophie is an orphan - the survivor of a shipwreck, found floating in a cello case and claimed by an eccentric bachelor, Charles. Charles raises her in the best goofily cinematic fashion: they write on the walls, eat jam for every meal, climb on the roof and replace formal schooling with lots of Shakespeare. Sophie doesn't even wear dresses - Charles gives her trousers instead, the crazy fool.
Well, naturally the Welfare people (a YA novel where the state is the villain? What are the odds?!) don't like this arrangement. Charles isn't raising Sophie as a lady and they're going to put her in an orphanage instead. Charles and Sophie do the sensible thing and scamper over to Paris, prompted, in part, by Sophie discovering a Parisian address in her cello case.