Ma Vie En Rose, Young Vic, London / How The Other Half Loves, Theatre Royal, Bath

Each year the Young Vic puts on a community show in which a cast of locals (of all ages) performs alongside professional actors and musicians. This season, they have opted to mount a piece inspired by Ma Vie en Rose, Alain Berliner's warm, funny and provocative 1997 movie about a seven-year-old boy who is convinced, despite all the evidence to the contrary, that he is a girl.

It's a good choice. The censorious suburbanites in the manicured district where the boy's family has just moved play a crucial part in the story. The director, Pete Harris, says the cast has fashioned "a show about a community, performed by a community, for a community" – a fact amusingly borne out when waves of the boy's family's middle-class neighbours descend on their housewarming garden party for regulation air-kissing and waltzes.

The piece dispenses with a script, and unfolds wordlessly in movement, mime and dance to a witty score by Gary Yershon. Seven-year-old Ludo is portrayed by a young adult, Adrian DeCosta, who captures the boy's shy humour and emotional openness. He's feminine without being effeminate. There are touchingly funny scenes where he tries and haplessly fails to copy the other kids in their gender-role games and where he and his chum Jerome (Ian Bonar) describe dreamy circles on a swing in boyish togetherness just prior to being caught in the mock marriage that incenses the neighbours.

I missed the film's Barbie doll-like mentor that presides over Ludo's imaginary world, and also its agonising comic twist. And the ending feels rushed: a sudden conga-line of mass acceptance that has not been properly motivated. But the show has some lovely touches: the tingling wonder aroused in our hero when a parade of his mother's dresses advances tantalisingly from the closets; the dippy game in which Ludo and tomboy Christine (Adura Onashile) swap clothes by tossing them at each other over the washing line. I will long remember, too, the sadness of the resigned gesture with which he lets his mother remove his dress, raising his arms as though waiting to be shot dead.

How the Other Half Loves was the West End success that made Alan Ayckbourn rich when it opened in 1970. Watching Alan Strachan's faithful, highly entertaining period revival in the Peter Hall season at Bath, I was struck by how this early comedy anticipates the procedures and preoccupations of the later Ayckbourn classics. There's the skill in deploying a technical innovation hand-in-glove with the theme. There's the disenchantment with the institution of marriage and the revulsion at male insensitivity towards women. And there's the fascination with a do-gooder who wreaks tragicomic emotional havoc.

Bob Phillips (Richard Stacey) is having an affair with Fiona Foster, his boss's wife. Rather than putting the two ménages side by side in a split-stage effect, Ayckbourn ingeniously superimposes them, emphasising how the two households are connected by adultery yet divided in every other way. Surreally occupying the same space, the snootily gracious Fiona (Marsha Fitzalan) in her moneyed, childless milieu keeps crossing paths with her victim: the depressed, housebound and betrayed Teresa (Claudia Elmhirst).

Ayckbourn complicates matters by having both disloyal partners use as an alibi their supposed concern with the fictitious infidelities of a third couple, the socially inept Featherstones. The highlight is the hilarious scene where this pair – tongue-tied Mary (Amanda Royle) and bullying William (Paul Kemp) – swivel on their chairs between two grotesquely contrasted dinner parties – one all well-to-do evasiveness, the other a drunken marital fight – that took place on successive evenings but are presented simultaneously.

The cast is spot-on, with Nicholas Le Prevost a joy as the blimpishly oblivious Bob. The play becomes a bit mechanistic in the second half, but Strachan's clear, buoyant orchestration and the two superimposed situations make the production a double delight.