Normally, a cast of four pipsqueaks would keep me miles away from any movie. I'm sort of allergic to the short-pants crowd. But Tokyo-born writer-director Koreeda Hirokazu brought us 1998's excellent After Life, which earns him the benefit of the doubt. Besides, in his new film Nobody Knows, the characters behave more like miniature adults than children.

Nobody Knows is based on true events that occurred in Tokyo in 1988, an incident dubbed "The Affair of the Four Abandoned Children of Nishi-Sugamo." The name pretty much says it all: Four kids, each by a different father, were illegally sneaked into a tiny apartment by their young, single mother, then abandoned. They lived on their own for six months, and until a tragic accident brought their existence to light, nobody else in the building had any idea they were there by themselves.

Inspired by this story and the larger issues it represented, Hirokazu started writing the screenplay for Nobody Knows 15 years ago. Back then, according to Japan's minister of education, there were 533 homeless kids in Japan between the ages of 7 and 14. By the time the script was ready in 2000, that number had dropped to 302, and Hirokazu worried that the film wouldn't have the same impact. But child homelessness clearly continued to haunt him, and he went ahead with the movie.

He spent a year filming, incorporating such spontaneous details as a squeaky pair of shoes one of the kids had worn onto the set and the growth spurts and voice cracks of his lead actor. The dialogue was mostly improvised; each morning the director explained to the actors playing the four kids and their mom what their lines would be. This gives the film a realistic, almost documentary feel, though it's filtered through the filmmaker's impressionistic eye. Of course, few documentaries—few films at all, for that matter—look this pretty. The kids are gorgeous, the colors are vivid, and bright white sunlight dapples even the grim confines of the small apartment where most of the story takes place.

As the film begins, Keiko (played by Japanese TV star You) and her eldest son, Akira (Yagira Yuya), age 12, are moving into a new apartment. They introduce themselves to the landlord, who pointedly says it's lucky Keiko has only a 12-year-old boy and not a bunch of noisy little ones. Keiko and Akira haul a couple of gigantic suitcases into the apartment; once inside, they open these to let out two more kids. Akira collects his third sibling from the train station that night. The four kids are instructed not to make any noise, and, except for Akira, they are not to leave the apartment. If they're discovered, they'll be evicted. They've never gone to school, have no friends and can't even think about playing outside. This alone would be a trial for the average youngster, but these kids seem to handle it serenely.

The next morning, Keiko, a cool but ridiculously childlike party girl, has vanished, leaving a note and some money. The kids are obviously used to this; Akira nonchalantly shops and cooks, and the oldest daughter does laundry and watches the other two half-siblings. They know Mom will come back, they just don't know when.

And she does come back, that time. But the children's self-reliance is put to the test when Keiko leaves again and fails to return for Christmas as promised. The money runs out, the power and water are cut off, and before long the kids are bathing in park fountains and outgrowing their raggedy clothes. The girls spend days huddled in despair. Sympathetic shopkeepers help with food, and Akira tries to get a job but is too young. It's clear the situation won't last long. Meanwhile, a combination of loneliness and hormones are fighting for Akira's attention; he starts to break down under the burden of playing dad when he should be playing baseball and video games.

The movie builds at a slow pace, and its two-and-a-half-hour runtime makes it drag in a few places. But it's worth sticking around for the final scenes; they're tinted with an almost inexplicable sense of hope, despite what has come before. You get the idea that, against the odds, these scrappy kids are going to be alright.

Nobody Knows

Rated PG-13. Cinema 21, 616 NW 21st Ave., 223-4515. 7 and 9:30 pm Friday-Thursday, March 4-10. Additional shows 1 and 4 pm Saturday and Sunday. $4-$7.