Kore-eda shot the movie in chronological order through four seasons from a script that changed every day. That's great for the movie's feel but bordering on a disaster for its structure. His accretive method simply isn't the most effective way to tell this story, which becomes randomly episodic as it goes on and on.

To start at the top of the list of missed opportunities, Akira can't be a full-fledged protagonist because his "responsibility" is conceived entirely in terms of Keiko's fault for imposing it on him. There's no tragic sense that if Akira weren't such a good boy, if he said to hell with it and let the haywire snap, they might be better off. (Akira tells the cashier that they were once separated by child aid services and that was a mess, but it's hard to say separation would be worse than what finally happens.)

You might also think that Akira displays a maladaptation many of us retain after childhood, clinging to what's familiar even when it isn't satisfactory. But without narrative structure, what you feel for these kids, and what you think of their situation and their reactions to it, can't rise to a very complicated level of drama. You feel bad for Akira, but you feel bad for the mistreated kids you read about in the paper; there should be greater dramatic payoff from the kind of access this movie affords us. I'm not sure Nobody Knows elicits more complex reactions from us than if Keiko had abandoned four dogs in the apartment. (Dogs are even more dependent and even less comprehending, after all.)

The most dramatically engaging part of the movie is watching the older children react to their mother--you can see them trying to be obedient and yet figure out how to get what they want. They're preternaturally good at reading her but too young to understand they have every right to escape from her screwy world; they've become experts at a horribly unnecessary skill. Once Keiko decamps for good, however, all that's left is the special pathos of childhood due to the fact that children have the capacity for suffering without the power to end it or even the consolation of understanding it.

Kore-eda then wraps the movie up with a sequence in which the children have a weirdly affectless reaction to a horrible household mishap. This doesn't even make the most of the pathos the movie has generated up to that point, but rather throws it away for a more anomic vibe. You could say that the point is that the children have become so conditioned to their life that they stop having natural feelings, but that isn't what we otherwise see and the lack of dramatic structure prevents Kore-eda from locking it in, in any case.