Just a few comments: I agree with the comments re the odd locution, "tiny city." We have lots of words in English that would be more appropriate and precise. Afterall, a thorp is a dorp. Also, the scientist parents would be bad scientists indeed to ignore the intriguing discovery of ruins, which are tangible and easily investigated and in themselves are not folklore. Are the existence of ancient peoples considered to be myth in the world of your book, or are you just being imprecise, and the attachment of supernaturalism to these ruins being questioned? I believe you should clalify this in your query. By the way, that moon hovering at the height of basketball rim gave me pause -- clearly this is a world outside of Newtonian physics. Maybe a phrase of explanation on this would be useful.
I also second the notion that following the chronology of the book may not be the best way to summarize your tale. The ruins seem to have the same function as the wardrobe in the Narnia books. A query to these books might begin: "The discovery of a magic wardrobe sends X and his siblings to a strange and frightening world."