When some filmmakers focus on children or childishness, they’re often just interested in nostalgia for childhood. The kids in Wes Anderson’s films and in a lot of movies Steven Spielberg produces are generic placeholders or evocations of other times and eras and experiences — loss of virginity, love of movies, discovery of a bygone world, precociousness as a means of self-flattery. It’s not always false. But with a director like Hirokazu Koreeda, you never feel a childhood being remembered or a quaint longing for a lost moment in time. Children are simply people. They have inner lives and worries and desires.

Koichi and Ryu, the two brothers in Koreeda’s new film, “I Wish,” are keen, curious, and blissfully, foolishly adventuresome enough to fall well shy of adulthood, which here is characterized by a kind of fecklessness, lassitude, and guilt. Neither brother has seen the other in a while. Their parents are young and splitting up. This means that Koichi (Koki Maeda), who’s about 12, lives with their mother (Nene Otsuka) at her parents’ home in Kagoshima, a city on Japan’s southern tip. Ryu (Koki’s little brother, Oshiro) lives with their father (Joe Odagiri), who shares a country house with the dudes in his band.