Mistress Masham's Repose

Mistress Masham's Repose is a children's novel by T. H. White, better known for writing The Once and Future King. It is set in the same world as Gulliver's Travels but in the present day at the time of writing (1946). Maria, the young orphan heiress to a sprawling English estate, runs across a colony of exiled Lilliputians while exploring its grounds. She then has to figure out how to stop her guardians from getting rich by selling them to circuses.

Tropes used in Mistress Masham's Repose include:

Antiquated Linguistics: The Lilliputians speak English this way, in a nod to their 18th-century origins (and because they haven't had much human contact since shortly after they came to England).
Big Fancy House: Malplaquet Manor is certainly big, and it used to be fancy, but the family's been broke for the last few centuries so it's falling apart.
Cloudcuckoolander's Minder: Cook to the Professor.
Conveniently an Orphan: Maria.
Eccentric Mentor / Genius Ditz: The Professor is quite good at medieval Latin as well as being the moral centerpiece of the book, but he epitomizes the Absent-Minded Professor stereotype.
Horse of a Different Color: The Lilliputians ride rats, as none of their horses made it out of Lilliput.
Illegal Guardian: The Vicar. Not only does he want to take the Lilliputians away (which could possibly be excused as merely looking after Maria's financial interests), but he's also actively embezzling money from her estate and plotting to disinherit her.
Lilliputians: Naturally!
Literary Necrophilia
Masquerade: The Lilliputians are the only fantastical element in the book, but the heroes end up constructing a miniature masquerade around them, as they don't believe they'd get a fair hearing if their story was made public.
Mouse World: The Lilliputians manage to live in one. They have some appropriately-scaled livestock, but mostly they improvise.
Numerological Motif: Numbers with calendrical significance recur throughout the description of the manor and grounds (for example, the manor has 365 windows, 52 state bedrooms, and 12 company rooms).
Old Retainer: Cook.
The Place: Mistress Masham's Repose is the small island that the Lilliputians live on.
What Do You Mean It's Not Awesome?: Maria's dialogue sometimes falls into this, being a bookish child without much social contact. For example, early in the book she thanks Cook for making her tea by saying:

"Cook, if you are ever captured by pirates, or surrounded by Indians, or if you should fall into the sea and be chased by a shark, I will see to it that this day's work is not forgotten, if it costs me the last drop of my blood."

What Measure Is a Non-Human?: Or a human who's six inches tall? The Vicar and Mrs. Brown aren't willing to think of the Lilliputians as human, and the Lilliputians themselves are worried that the law would agree.