The Legend of Zelda: The Minish Cap/Fridge

Fridge Brilliance

 * The cap itself lets you shrink down to the size of the epynonymous Minish. If you say "the Minish" quickly enough, it ends up sounding like "diminish", or to shrink.
 * The byproduct of the Minish only being seen by children: the most prominent forest-dwelling race is/are the Kokiri/Koroks, who are stated to never grow up; the largest group of Minish live in the woods. No matter how much time passed, they would always be able to communicate.

Fridge Logic

 * The Picori and their creations are Invisible to Adults. Fridge Logic dictates that if the Picori were truly only visible to children, they would merely be the in-universe equivalent of an urban legend. A significant number of people in the game believe that the Picori exist. Therefore the invisibility effect is either something that the Picori are doing themselves as a form of protection and can be "switched off" at will, something that can be circumvented with Magitek, or both. Afterall, people could see Vaati just fine. Presumably the Picori's re-sizing magic (the hollow tree stumps, etc) also cancels the invisibility, meaning that the invisibility can be countered comparitively easily by anyone who can use magic.