I think Melancholia (2011) would be a cinematic double whammy for kids: it’ll bore them stiff with its glacial pace and melancholic, artsy vibe, and scare the bejeezus out of them with a doomsday plot about a mysterious rogue planet colliding with Earth. That’s a real two-fer if your parenting strategy involves punishing with equal parts extreme boredom and existential dread.
My vote is Picnic at Hanging Rock. Very slow moving, and nothing really happens.
I ruled out Tarkovsky when the OP specified “mainstream” and “no experimental art films or surrealism.” But if he’s in the thread with Andrei Rublev, you have to consider pretty much his entire body of work. I’m particularly fond of Stalker, but that’s just me.
I’ll see your Picnic at Hanging Rock and raise you Walkabout.
Just a minute, Walkabout has Jenny Agutter in the buff somewhere in there, doesn’t it?
Technically, yes, but a distant shot IIRC, much further away than the poster would lead you to believe.
The Sorrow and the Pity (as it plays a role in Annie Hall).
Four and a half hours, wasn’t it?
Never seen it, but what about QB VII?
Someone has beaten me to it but I want to mention
Lawrence of Arabia
Some amazing music and photography but is nearly four hours and they even had to throw in an actual musical interlude half way through. A youngish kid would be bored stiff.
And there is…
Les Miserables
I’ve never fallen asleep in a cinema but this is the one that nearly caused me to break that duck. Unbelievably tedious (and soul-destroyingly downbeat) as an adult; I can’t imagine any child finding it otherwise.
I did! It had some helpful tips like:
- Wear/bring your shoes in the event of a building evacuation
- Only use stairwells for orderly evacuation
- Do not evacuate to the roof unless ordered to by emergency personnel on scene
Timeless tips for any office environment.
Tripler
It wasn’t until one of my mountaineering courses that I got the “Fire Hose Expedient Rappelling” training.
You missed some:
- when working with a multi-lingual team, provide instructions in English for clarity
- ‘two is one and one is none’; keep a spare store of all mission-critical components in a second location
- when negotiating a deal, bring something of value to the table besides yourself
- always personally inspect the state of operation of equipment before attempting use
- remove all jewelry before working with rotating machinery or being taken hostage
Stranger
I mentioned Andrei Rublev because it was on DPRK’s list. I don’t know if it was an experimental/art film in the Soviet Union, but it might have been. It certainly qualifies in terms of tediousness.
When it comes to Masterpiece Theatre, I nominate Anna Karenina as being the all-time winner in the sleep-inducing category. I hate the novel too.
I think The Spy Who Came In From The Cold could bore any kid stupid. Even if you understand Cold War politics and espionage, it’s pretty much just talking and maneuvering.
I like it, but I can see the “tedious” criticism, so I won’t defend it. But I think Tarkovsky is best known (to the extent that he’s known), at least in the US of 2025, as an art-house filmmaker, even if someone wants to say “experimental” is arguable. There’s certainly further-out-there stuff than his. At any rate, I’d have to argue that he’s certainly not mainstream.
A Dandy in Aspic falls into the same category.
QB VII was made for TV and starred Ben Gazzara and Anthony Hopkins as the novelist and the physician, respectively. I quite liked it, but it took enormous liberties with the book. I recommend that anyone who wants to see the movie should read the book first.
The movie, BTW, is quite long and was aired on at least two consecutive evenings when I saw it on British TV.
In both cases the stars were mostly comedians.
I think older kids would find Being There (1979) slower than a snail napping in molasses. Chance the Gardener (brilliantly played by Peter Sellers) doesn’t do anything—he’s definitely no Iron Man. There’s no big journey, no transformation arc. He just is.
The humor’s bone-dry, built entirely on grownups mistaking his plain talk about gardening for some kind of deep Zen insight. But to a kid, that just sounds like “blah blah blah plants, blah blah blah dirt.”
That said, little kids—or perhaps even a few Dopers 
—might actually vibe with Chance. He speaks slowly. He uses easy words. He talks about plants. He’s not dumb—just tuned into a different frequency. For young kids, he might come across like Mr. Rogers: “Finally! Someone who talks my language”
So what kind of awful thing did your kids do to deserve this kind of punishment?
They didn’t take my gardening advice.