According to an article in the 9 October 1974 edition of Variety, this film was watched by President Richard Nixon on his flight home to California after he resigned the presidency in August of 1974. He reportedly enjoyed the picture.
Mrs. Frankweiler makes a phone call sitting in front of a marble fireplace after sending the children to wash up before lunch, carved into that fireplace are the words, "A coeur vaillant rien d'impossible". This French phrase roughly translates to "nothing is impossible for a willing heart".
Claudia's chosen bedroom - the bedroom from the Palazzo Sagredo in Venice - is still on display in the museum in 2021, located in Gallery 507.
Claudia and Jamie are depicted as walking from the museum to the Central Park Carousel - a distance of a little over a mile. Later, they presumably walk from the museum to the General Post Office on 8th Avenue - a distance of over 3 miles.
Mrs. Frankweiler has Claudia read part of the poem "The Road Not Taken" by Robert Frost (1874-1963), published in 1920.