Movies like The House with a Clock in Its Walls

If you want that specific blend of whimsical-but-creepy mansion mystery with a young protagonist learning magical rules on the fly, The Spiderwick Chronicles and Nightbooks probably nail it best—they share the same tone of wonder mixed with genuine threat and the pacing of discovery. The Borrowers might work if you're after the Victorian architecture-as-character element and that slightly gentler supernatural intrigue, though it skews less dark. You'd be taking a real tonal shift toward full gothic dread with Flowers in the Attic or Curse of the Crimson Altar, so only pick those if you're ready to lose the warmth.