I really like the basic concept here and it can easily be used in just about any decent amusement park or arcade. Very inspiring and very suitable for the game and time period!
I realize that what you've written there is basically synopsis, rather than a complete mystery, but I do have some concern with the idea that the Queen's Nose has to be saved for the ride. I don't know what your local arcade offers in terms of rides, but is the Ghost train the only place the token can be used? That may just be suitable enough, but for a more general mystery I would suggest that the Queen's Nose can be used in, say, four different rides and the event triggers in an appropriate fashion for that particular ride.
If you have any additional suggestions on hurdles to throw in the kids way while they're small, that'd be interesting too and perhaps some more info on how to transform back. What are they supposed to do with the Queen's nose once they retrieve it? Go on the ride again or did you have something else in mind?
Should I use this scenario on my own I'd have to come up with a few more details and if you already have such ideas, based on what your players did for example, I think that would help a lot.