Meitantei Conan

Kudo Shinichi is a seventeen year-old high school detective whom people call the "Modern Sherlock Holmes." However, one night after a date with his childhood sweetheart, Ran, Shinichi witnessed an illegal trade and, caught off his guard, was knocked unconscious and fed a drug that was supposed to kill him... but he woke up and found himself shrunken to a seven year-old. In order to track down the men who did this to him, Shinichi hid his identity and lived with Ran, whose father happened to be a hopeless detective, and with that came a series of murders and mysteries that he must solve.
(Source: Anime News Network)

Note:
- Includes Keisatsu Gakkou-hen - Wild Police Story in episodes 1029, 1038, 1042, 1061
- Episodes 11, 52, 76, 118, 162, 184, 208, 342, 356, 449, 452, 487, 488, 489, 490, 515, 516, 521, 522, 651, 734, 804, 805, 927, 928, 1187 aired with a runtime of ~50 minutes as opposed to the standard 25 minute long episode.
- Episodes 96, 129, 174, 219, 263, 304, 383, 479 aired with a runtime of ~90 minutes as opposed to the standard 25 minute long episode.
- Episode 345, 425 aired with a runtime of ~115 minutes as opposed to the standard 25 minute long episode.