- Life Imitates Art: There is no real "Angel" statue,note but in 2009, the Met acquired a small marble cupid likewise reputed but unconfirmed to have been created by Michelangelo. Both the statue and the circumstances are very similar to the ones attributed to Angel in the story. The book even references a long-lost Michelangelo cupid that may very well be the one currently on display. In an Author's Note to the 35th anniversary edition of the book, the author herself remarks on the coincidence and evokes this trope by name.
- Technology Marches On: While even a museum like the Met wouldn't bother to put a security system on every exhibit, the rise of affordable and effective CCTV cameras and motion-activated alarms would insure that Claudia and Jamie wouldn't have lasted a single night there now...much to the disappointment of modern children who still view the book as a perfect fantasy of running away.
- Values Dissonance: The idea of two suburban kids running away to New York City would be terrifying today, and it's doubtful that even in NYC, two children could wander around on their own without at least being questioned by an adult. Even an eccentric millionaire like Mrs. Frankweiler would more likely call the police immediately rather than invite the kids in for lunch.
Trivia / From the Mixed-Up Files of Mrs. Basil E. Frankweiler