If Joaquin Phoenix had failed to turn up in an artfully dishevelled beard, director Mike Mills’s fourth feature would still easily qualify as his shaggiest to date. A hipster reworking of Uncle Buck without the jokes and John Candy, it’s cuter than that sounds, albeit a little too cute at times; even mental illness gets a polar bear retelling.

We are being churlish. It takes Mike Mills approximately five years to make a feature and when he does, they are treasure troves of autobiographical themes and lovely flotsam. In 2010 he wrote and directed Beginners, based loosely on his father, who came out as gay after the death of Mills’s mother. In 2016, 20th Century Women chronicled his relationship with his mother.

C’mon C’mon was inspired by Mills’s son Hopper and is embroidered with lovely things such as The Wizard of Oz and music by The Primitives. It stars Phoenix as Johnny, a New York-based radio journalist who, throughout the movie, records interviews with kids about their lives, asking such questions as “What makes you happy?”

For all his experience as a documentarian, Johnny is poignantly single, still reeling from the death of his mother and estranged from his sister and nephew, until the latter two face a family crisis. When Johnny’s sister (the marvellous Gaby Hoffmann) has to follow her bipolar father (Scoot McNairy) to San Francisco to assist with a manic episode, it falls to Johnny to take care of her nine-year-old son, Jesse (the naturalistic Woody Norman), a kid with a family in flux who responds accordingly.

Mills’s domestic partner is the filmmaker Miranda July (Kajillionaire) and Jesse’s quirks, notably pretending to be an orphan, will feel familiar to fans of July’s early work, particularly You and Me and Everyone We Know. His is not an unhappy childhood but it is a time defined by strife and sadness, a discontent that causes him to act out; if only a little.

C’mon C’mon is certainly heartfelt, but it lacks the lovely levity that defined Mills’s earlier films. Phoenix is as understated as his Joker was large;he has to be to keep pace with Norman’s subtle performance. Cinematographer Robbie Ryan’s lush monochrome photography brings an authentic gloss to material that explores intergenerational bonding without manufacturing anything like a Hollywood ending.