One of the fundamental differences between children and adults is this: Children do what adults stew about. A child is angry with another kid, he hits him; the next day, they may well be best friends again. What happened yesterday is in the past, forgotten.

Not so with adults. When they have a problem with another, too often they brood on it, carry the burden in their minds and in their hearts, look for insidious ways to get even, to make sure they come out the winner in the end.

Take “Carnage” as an example. Two kids got into a bit of a tussle at the playground; one hit the other with a stick. Now all four parents are involved.

They’ve come together, allegedly to talk it out, put it behind them—but in reality to point fingers, to assign blame. What started as a small mess has escalated into a much bigger mess—and while it may be a realistic mess, it’s never a very interesting mess.

The cast is first-rate, but the characters are too similar and, in fact, over the course of a long conversation that just seems to go in circles, they all trade places on the merry-go-round until, in the end, they all seem to be riding the same horse.

Director Roman Polanski knows how to make movies that build tension, but here he builds nothing but a big argument that is, for these four people, worse at the end than it was at the beginning. This is all “sound and fury signifying nothing. . . .”

We begin on a New York City playground. As the opening credits roll, we watch two 11-year-olds, Zachary (Elvis Polanski) and Ethan (Eliot Berger), begin shoving each other. Their disagreement escalates; Zachary whacks Ethan with a stick (it actually looks like he misses, so the play probably had to be “reviewed in the booth”), damaging his face, knocking out two teeth.

Ethan tells his parents, Penelope (Jodie Foster) and Mike (John C. Reilly), what happened, and they invite Zachary’s parents, Nancy (Kate Winslet) and Alan (Christoph Waltz), to their home for a discussion.

Talk begins politely enough. Penelope would like Zachary to apologize, and Nancy is all for that: Alan will tell their son he has to apologize; she’ll bring him by that evening.

But that’s not good enough for Penelope; Zachary should apologize because he wants to, not because he is told to.

They need to discuss this further. Mike invites everyone in for coffee and dessert—“Penelope makes great cobbler”—and what began as a “kid problem” now devolves into an adult verbal brawl.

Penelope becomes strident, Mike supports her; Alan is constantly on his cellphone, taking calls from his office, driving everyone to distraction.

Nancy starts out being conciliatory, trying to put this behind her; then she gets sick, then angry, and lashes out at Penelope and Mike, which causes them to lash out at her.

Mike brings out some 18-yearold scotch to settle everyone down and the alcohol further loosens tongues. Cracks are now showing in the two marriages; husbands attack wives, wives berate husbands; the guys band together, then the women find common ground; then everything comes apart again.

Neither the arguments nor this movie are headed anywhere except in circles. The film is based on a play and looks it. There’s so much talking, so little action until, mercifully, we’ve left the apartment, left the two couples to their own misery and are back on the playground the next day where . . . oh, isn’t that just like kids?