Kimya Dawson, Union Chapel, London

Even the Juno effect can't help

"I feel like I don't have the charisma," Kimya Dawson plaintively mumbles. "I can't play my guitar and look at you at the same time." It must be a relief that her songs have reached No 1 almost anonymously, on the soundtrack to the film Juno, put there by its teenage star Ellen Page. The 35-year-old Dawson already had a decade's work behind her on New York's anti-folk scene, largely as one half of The Moldy Peaches with Adam Green. But nerves that make her murmur and apologise before songs still have her hunching defensively over her guitar.

Anti-folk's inclination to child-like inconsequentiality is given free rein as Dawson starts with eight songs from her new children's album, Alphabutt, written for her own baby daughter, busily taking her clothes off in sight of her at the front here tonight. "The poop and pee songs – what's wrong with me?" she wonders aloud. And while it is fine for a songwriter with a young child to write for the kindergarten, you have to wonder why her adult audience are whooping and giggling. If Paul McCartney were to try the same trick, these same indie hipsters would form a hunting party.

Her scene's seemingly bottomless indulgence and willed innocence is a retreat from crass commercial instincts in the wider world, where every value can seem for sale. But as the crowd happily suggest animal noises, and Dawson's lyrics switch between childhood and old age, twee regression sets in.

The scene's ethics are partly dissected on a later song, "Singing Machine". "Doesn't matter what you look like, doesn't matter what you sound like, doesn't matter if they like you," she advises would-be musicians. "Just remember to be kind." This combines UK punk's participatory ethic with US enthusiasm, like a lo-fi American Idol. Self-criticism, you suspect, is her mind's default position. But, having summoned the bravery to get on stage at all, applying it to music seems too painful. Limpness results.

"Loose Lips", a vibrant song against authority, shows Dawson's capacity. "We won't stop until somebody calls the cops. And even then..." she declares, as she combines anti-Bush rhetoric with loving support for a self-harmer, and undefined nostalgia for "how it used to be". The child night-panics and fear of being entombed in "Underground" dig deeper into her. Her first song "Eleventeen", written when she was "kind of a mess" from drugs and depression, then sees her head bow low as if singing to her old self, lost back in that place. You can't say she's insincere.

When two teenage girls apologetically leave early, one hanging fiercely to the hand of the other, Dawson politely says goodbye. "Nice meeting you – you have school tomorrow?" she enquires. Pop is built from such intimate connections, and she is concerned with community. Perhaps these were new fans as attached to Page's witheringly sarcastic, super-hip fellow teenager from the film as to Dawson. But the latter's songs helped build the soft, warm-hearted character that the script at first conceals. Her simple, looping chords and slightly shaky, girlish voice are the template for even incidental music, and inform Juno's whole texture. There is, though, a steady drift from the Union Chapel's pews before the hour-long set's end. And not everyone has school.

The Juno effect won't phase someone who can observe: "If you hear anyone say, 'You are huge', look at the moon." But the sudden whirl of creative ambition in "The Beer", a fantastic tale of violent suicide and subsequent zombie visits to the mall, frustrates in its rarity. One of a brace of moving new, adult songs about her baby daughter casually admits her songwriting will probably deteriorate because of her. "All I can do next is be a good mother," she states, knowing there are more important things than music. Except that, when you're performing, there really shouldn't be.