There are several moments when Mary (Margaret O'Brien) refers to her servant in India. When watching the film, one hears the word "servant", but Mary's mouth is clearly forming the word "Aya" as in other versions of The Secret Garden.
Dickon is supposed to be around the same age as Mary and Colin (10 years old), but the actor who portrayed him, Brian Roper, was about 20 years old at the time of filming. Margaret O'Brien and Dean Stockwell also were a few years older than the characters they played.
The song that Mary Lennox is singing when she is discovered by the British officer (who tells her that her parents are dead) is the love song from Nacht über Indien (1939), when Tyrone Power is showing Myrna Loy around an Indian school and is falling in love with her. It also haunts him the moment before he is escorted to his coronation.
In this film, Manchester-born George Zucco, the slimy mad doctor or smooth-talking villain of so many horror and mystery films (e.g., Prof. Moriarty in Die Abenteuer des Sherlock Holmes (1939), Charlie Chan in Charlie Chan in Honolulu (1938), Der Glöckner von Notre Dame (1939), The Mummy's Hand (1940), Das Grab der Mumie (1942), The Mad Ghoul (1943), Voodoo Man (1944)) has one of his few sympathetic roles as the kindly Dr. Fortescue.
Though a noteworthy MGM adaptation of the acclaimed 1909 childhood tale by Frances Hodgson Burnett, this film, complete with three Technicolor sequences, failed to garner a contemporary New York Times review.