Surprisingly Functional Toys

When a character is shrunk or is naturally under three inches tall and said character encounters a recognizable object scaled to the character's new size, said object will retain the function and properties scale of its original size. In short, dollhouse sized props work for dollhouse sized people, Square-Cube Law and Law of Conservation of Detail be damned. This is much easier to Hand Wave away in stories that involve shrinking characters, since some type of magic or pseudoscience is obviously already in play.

If an honest-to-god toy is manufactured to be functional, it's My Little Panzer.

Examples of Surprisingly Functional Toys include:

Anime and Manga

Justified in a Doraemon Non-Serial Movie - a pint-sized alien crash-lands near Nobita's house, and Doraemon uses his pocket full of goodies to create a fully functional living space out of one of Shizuka's dollhouses.
Somewhat inverted and played with in Ponyo on the Cliff by the Sea where, instead of shrinking, a toy boat is expanded until it's big enough to carry two young children, and works perfectly well. This is all part of the magic, of course. Played with when a couple of items are left in the boat when it shrinks back, really do become perfect miniatures.

Film

Night at the Museum runs into a lot of this with the Roman and Western displays, presumably HandWaved due to the tablet magic. (Though that doesn't explain the RC car.)
- Averted, however, with Jebediah's useless plastic guns. "Now you know Jebediah's secret shame."
- The sequel has a fully functional model plane, and judging by the urgency involved in trying to stop it, a space rocket. Bear in mind they're at the Smithsonian.
In Alvin and The Chipmunks The Movie, Simon's glasses were from some sort of toy Santa. In the unlikely chance that they even had any sort of "lenses" they wouldn't be made to help vision.
Beetlejuice. After Adam is shrunk down to a couple of inches tall, he drives a toy truck that handles and sounds like a real truck. On YouTube at 5:15.

Literature

Stuart Little, where Stuart drives an RC car around, as opposed to the book version, where it was custom made.
The Mouse and the Motorcycle by Beverly Cleary, where the eponymous mouse is able to make a toy motorcycle go by making engine noises.
Averted in The Magicians of Caprona. Two characters have been shrunk and put in a dollhouse, and before they realize what's happened, they wonder why nothing in the house works.
Justified in The Indian in the Cupboard series; toy objects don't work as they are, but can be turned into functional versions of themselves through the same "magic of the cupboard" that brings toy people to life. For example, putting a toy doctor's bag in the cupboard turns it into a fully-stocked medical kit, and toy guns (unfortunately) turn into functional guns.
Averted in the Miss Bianca series of children's novels (the inspiration for The Rescuers). In the novels Miss Bianca is the pet of an ambassador's son, so she lives in a dollhouse, but most other objects are not simply mouse-scaled props, but are indeed fabricated from other objects. For example, spools of thread are used as chairs, the salt shakers are really thimbles with bottoms attached, combs leaned against piles of books are staircases, and so forth.
- This happens in the movies as well a bit, but most of the props there are literally shrunken versions of human objects.
Used with a normal sized protagonist in Stephen King's Eyes of the Dragon. The main hero is framed for murder and imprisoned at the top of a tower. He convinces his jailers to let him have the doll-house he used to play with as a kid to help pass the time, then proceeds to use the fully functional, though tiny, spinning wheel it contains to fashion a thin rope out of threads from the napkins he's given with every meal. Justified as when the doll house was first mentioned, special note was made that his father had made sure everything in it was constructed as realistically as possible.

Live Action TV

Semi-averted in Doctor Who episode Night Terrors; the dollhouse itself is way too realistic, but contains fake food and wooden frying pans.
Inverted in an episode of Lost in Space; the Robot somehow becomes huge and inexplicable contains rooms you can walk around in and human-sized equipment like tape drives.

Newspaper Comics

In Peanuts, Schroeder's Piano is a toy, but plays like a grand.
- The black keys are actually non-functional. When asked how he manages to play as well as he does, he replies with "lots of practice."
  - That must also be how he makes it sound like three different kinds of keyboards in A Charlie Brown Christmas.

Video Games

In The Legend of Zelda the Minish Cap, Link's equipment stays with him as he grows and shrinks. Some things, like rupees, are the same size relative to Link, regardless of how big Link is!
In Harley's Humongous Adventure, he got parachutes, dynamite and toy tanks.

Western Animation

In the Looney Tunes short "Feed the Kitty", the kitten Pussyfoot manages to "hotwire" a toy wind-up car and drives it around erratically.
- As a tribute, director Joe Dante has Gizmo do the same with an RC car in Gremlins.
Averted in Foster's Home for Imaginary Friends, an imaginary friend tries to drive a toy car only to realise it doesn't work that way.
In the rare times that Pinky and The Brain interact with other civilised mice ('The Third Mouse' comes to mind), toy cars end up acting this way. When they try it in 'A Pinky and the Brain Christmas', it's subverted: it's an RC car, and they don't have the remote themselves.
ReBoot has a game where the characters are the size of dolls. The User character (also doll sized) used cars and a plane that were fully function. Since the context here is a video game, it's excusable.
The Penguins of Madagascar has the turtles use many strange toys in Kowalski's inventions, but they have a pink toy car that at first doesn't seem to have been altered at all, but still functions like a real car.