In Ira Sachs’ well-done new film, “Little Men,” two very different middle school boys become fast friends when a development in Brooklyn real estate pulls them near each other.

Theo Taplitz plays Jake, a reserved, artsy wallflower who fills up sketchbooks in class, drawing dresses for the girls around him. When his grandfather dies, he moves with his parents Brian (Greg Kinnear) and Kathy (Jennifer Ehle) from hectic Manhattan to Grandpa’s old building, which is bigger, quieter and, most important, rent-free. Just below their new home is a storefront clothing shop run by Leonor (Paulina Garcia), a Chilean seamstress.

Her likable, street-smart son Tony (Michael Barbieri) immediately gets chummy with Jake. Soon they’re having fun and traveling the sidewalks side by side, Jake on his Rollerblades, Tony on his kick scooter, fast friends sharing their maturing wishes and small worries. It’s the kind of realistic New York story that Sachs does well — quiet, carefully detailed, never melodramatic for a moment.

Of course, no youth is free from challenges, and what hits the pair is unexpected and painful. Brian is a so-so stage actor. The family has relied on Kathy’s income as a psychotherapist for years. To those two classic New York careers, they now add a third as Leonor’s landlords. Brian’s late father adored her and long kept her rent at a rate that’s a fraction of what the upscaling area now charges. Jake’s parents have to deal with the situation, and invite Leonor to have a chat. She knows what they want to tell her and is always just too busy at the moment.

A restrained family feud begins. Jake and Tony, deeply loyal to each other and unwilling to be pulled apart, punish the elders by going silent. They are mute whenever their parents want them to speak. It’s a sort of selective disorder that’s often associated with anxiety, and it pushes the parents in that direction, as well.

Sachs is a wonderfully humane filmmaker. There are never out and out saints or demons in his films, but richly detailed, relatable lives offered for us to understand. The fact that Leonor spends her days on the ground floor beneath Brian and Kathy’s new apartment is a subtle symbol of the upper-class, lower-class gentrified division they have moved into. She is cautiously reserved when she is invited to visit her new neighbors, aware of who occupies which level of status.

Kinnear is touching as he explains the financial difficulties of his career as a struggling actor. He never behaves like a class-warfare villain. He raises his voice only when he’s endlessly goaded by the silent Jake and Tony, telling them that parents are people, too, just trying to do their best. He’s a longtime New York resident relieved that he no longer has to pay the city’s rising rent while expecting a fair amount for his own property, a complex role he performs with full credibility.

Sachs is very effective at summing up other differences between the adults and their children, giving us hints and encouraging us to fill in the details. Jake is often filmed while standing near rainbow-striped backgrounds. He’s too introverted to announce that he’s growing up gay, but his classmates catch him on their radar, calling him “Katy Perry” as he skates past them. When the boys attend a crowded after-school dance party, Jake’s expression watching Tony from afar says nothing and everything. I imagine many moviegoers will develop a bit of a crush, too. Barbieri is a natural entertainer. I’m looking forward to seeing him return with his upcoming role in “Spiderman: Homecoming.”

The film feels a bit slight. Some passages, like a long improvisational shouting match in Tony’s acting class, seem to be there because they’re charming, not because they’re vital to the story. But this is an excellent portrait of three-dimensional children and adults, warts and all.