Oh shit, I just realised: I took my nearly-3-year-old niece and nephew to see Hey Duggie a few weeks ago.
It's a kids TV show but they put a bunch of episodes together for a cinema version. It's about an hour long. The twins were starting to get antsy after like 45 minutes, so we left. They did pretty well considering it was their first time in a cinema, but I guess that would technically be the first time I left a cinema before the "movie" finished (even if it wasn't really a "movie" of the kind TC meant).
Not to be confused with XIII_Minerals.