Billing Displacement: While Kris Kringle is definitely the story's central character, Edmund Gwenn was billed third behind Maureen O'Hara and John Payne in the original film. This wound up paying off for Gwenn, who was nominated for (and won) the Best Supporting Actor Oscar.
Enforced Method Acting: Natalie Wood really did feel surprised when she tugged at Kris Kringle's beard, and saw him naturally react in minor pain.
Executive Meddling: The film was originally released in May despite being a Christmas film, due to an executive that believed people were more willing to see movies in May instead. This famously led to a marketing campaign that hid the Christmas themes of the film, including a trailer that instead of showing the film showed a fictional producer trying to figure out how to sell it while other contemporary stars raved about it. Fortunately, the film turned out to be a massive success anyway and actually ran long enough that it was still in theaters when Christmas actually rolled around.
Keep Circulating the Tapes: The 1973 made-for-TV remake has yet to receive a DVD release. However, Netflix did have it for streaming.
Playing Gertrude: Maureen O'Hara was 27 when the film came out and played the mother of a 8-9 year old Natalie Wood.
Unintentional Period Piece: Which leads to a case of Hollywood Law in the 1994 remake when it sticks too closely to the original's story, as after 1975 it would only be necessary to prove Kris wasn't a danger to himself or others, rather than entirely disproving that he was mentally ill.