Steven Spielberg once said that if you over-rehearse child actors you risk a bad case of the cutes. But it may be even more of a risk with very natural child actors and their accomplished adult co-stars in beautiful black-and-white films in love with their own emotional literacy.

Mike Mills’ C’mon C’mon is a swooningly photographed drama about a radio journalist and adorable guy in middle age called Johnny, played by Joaquin Phoenix – part of the great tradition of journalists in the movies in that his employer requires of him just one big apparently open-ended task. He and a colleague are travelling around the United States for what amounts to a substantial oral history project, interviewing high-school teenagers about what they think of their lives, their families, their communities and their futures. Johnny is single, having just split with a long-term girlfriend: he is smart, funny, dishevelled and paunchy – and a good listener to the kids whose honesty and intelligence he admires.

But Johnny has a serious family problem: he has fallen out badly with his adored sister Viv (Gaby Hoffmann) and hasn’t spoken to her for a year, since the death of their mother; Viv is angry with him for being irresponsible and failing to do any of the emotional heavy-lifting. But now Viv needs him: her semi-estranged partner Paul (Scoot McNairy) is bipolar and having a very serious episode, and Viv has to get him into a facility. She needs someone to look after their precocious eight-year-old son Jesse, played by Woody Norman in a supernaturally heart-tugging performance.

So Johnny, the wacky cool uncle, offers to shoulder the burden of being a real adult for once and take Jesse to New York while he interviews another batch of high-schoolers; soon he realises what a challenge being a parent is. This will be maturing experience for them both, and Johnny records reflective audio-diary entries with the same big fluffy microphone he uses for work. Occasionally, he reads aloud from classy books whose authors and titles are flashed up on screen in austere sans-serif capital letters.

All in all, C’mon C’mon is an impressively contrived film, almost a machine for winning awards, a monochrome reverie of midlife yearning.