First Night: Tusk Tusk, Jerwood Theatre Upstairs, Royal Court, London

Youngsters carry off remarkable stage debuts

It's nearly two years since Polly Stenham made a sensational playwriting debut with That Face in the Royal Court's upstairs studio, a piece about a dysfunctional middle class family, with a drunken mother who made Jocasta look like a wilting violet, that won every "most promising" award going and transferred, admittedly with limited success, to the West End.

The difficult second play syndrome has not proved a curse. Tusk Tusk is another coruscating, highly skilled piece of work, with an equally disastrous maternal figure who has gone missing. The title is an oblique reference to that favourite nursery song "Nellie the Elephant" who packed her bags and said goodbye to the circus. Her children have to fend for themselves on £200 in the new apartment, surrounded by packing cases, adopting a tribal lifestyle that has elements of Lord of the Flies and Where the Wild Things Are.

Again, Stenham reveals a natural talent sensibly dedicated to telling what she knows about. 15-year-old Eliot and 14-year-old Maggie – played, in remarkable stage debuts, by 17-year-old Toby Regbo and 16-year-old Bel Powley (whose sweet face you'll recognise from the recent TV Little Dorrit) – are holed up with their seven-year-old brother Finn (nine-year-old Finn Bennett, no less than extraordinary).

Finn, like Maurice Sendak's Max in Wild Things is always being sent to bed with his jungle fantasies, while Eliot is blowing the loot on alcohol and trying to impress a new girlfriend – Georgia Groome as Cassie – and Maggie is pretending to be a Polish nanny when the upstairs neighbour shouts through complaints about the noise.

Things turn a bit raw with Finn suffering a bad accident and the stage is transformed by designer Robert Innes Hopkins into a birthday party environment that is invaded by well meaning friends Katie and Roland (Caroline Harker and Tom Beard). It turns out Roland was more than just friendly with Mum – who's some sort of psychotic, drug-addled man magnet. Dad died of cancer, social workers are probably on red alert.

Mum has been missing for a week, so the situation has not yet spiralled out of control into the realms of implausibility, though Stenham is not too worried by that consideration in her conclusion. The point is she has found a tone both authentic and powerfully demotic for these mixed-up brats – yes, you do want to bang their silly spoilt heads together – and devised a scenario that keeps the mawkish poetry intact.

She's very good at controlling the release of information and sustaining dramatic tension, and her director Jeremy Herrin has not only cast the play brilliantly, he's also proved again – as he has done with David Hare and T S Eliot – that he knows how to find the proper rhythm for stage dialogue and maintain that fluency; there's a terrific soundtrack of barbaric indie rock by Emma Laxton to help him along.

It's a big ask of the young actors to complete the journey – Finn has constructed a cardboard boat, Max, by the end – but they carry it off superbly, and there's nothing but a feeling of both dread and concern as the new day dawns and the sun dapples the brickwork in the outside garden.