THEATRE The Red Balloon, Olivier, RNT

Small children can be bracingly heartless. There was I, wrestling with a lump in my throat as a mysterious red balloon - which had palled up with Pascal, a lonely little Parisian boy - is murdered by the pack of school bullies and slowly deflates before his stricken gaze. Behind me, though, a young lad was wrestling with a sense of grievance. "But it hasn't gone bang!" he exclaimed in an aggrieved, loud whisper. He'd had preferred a bang for his buck rather than all this sentiment. Do we believe in fairies? No, we don't: pull her wings off.

Of course, the above spectacle is itself a reminder of the cruelty children are capable of. Watching Anthony Clark's musical stage version of Albert Lamorisse's short, largely wordless Fifties French film, I kept thinking: haven't we been here before recently at the National? Adult actors playing children; victimisation; the pack mentality. Substitute a squirrel for the balloon and it's Dennis Potter's Blue Remembered Hills. Red Remembered Balloon? That would be pushing it, perhaps, though Clark's adaptation leaves you in no doubt about the unloveliness of Pascal's contemporaries, as the gang chases him round the huge bridge, cantilevered out into the void, on Ruari Murchison's set. In a comically horrible touch, one of the more sadistic girls uses her large catapult as a divining rod for locating their prey. The two sticks, threaded with almost invisible strings, by which handler Malcolm Shields, controls the pushy, anarchic movements of the red balloon, also has the look, at times, of divining rods. At others, he seems like a double-batoned conductor - but always unobtrusively. If this is a show that "bares the device", it does so without puncturing the illusion.

The haunting bits worked better for me than the comic business, and to judge from the laughter rate of my six-year-old assistant, that goes for her, too. The balloon's butting antics produce some mildly funny physical farce at the school with the bereted caretaker and nubile blonde-wigged teacher thrown by it into some Benny Hill-like situations. On the verbal front, the scene with Pascal's bickering parents in their no-pets rule flat relies heavily on children's Pavlovian delight at hearing the word "poo": "The cat's done a poo on the carpet."

It's in sequences such as the charming "Umbrella Song", in which Pascal seeks brolly shelter for himself and his balloon from Parisians tripping by in the rain, that the show achieves lift off. Mark Vibrans' music isn't exactly bursting with inspiration, though it has a nice line in unforced poignancy. The pure, piping voice of the actress Nicky Adams, who plays Pascal with a moving earnestness and lack of self pity, does this handsome justice.

One good thing about the piece is that, unlike a lot of children's shows, it doesn't give you a neat doggy-bag moral to take home, or a physics lesson. What does the red balloon represent? What does it mean when Pascal is joined in his grief by all the balloons in Paris and lifted away into the air? Unlike balloons, these are questions you can pop again and again.

Tues, Thurs, Fri matinees to 30 Aug (0171-928 2252)