Stand-up comedy for kids: it's one of those ideas, like cardboard milk cartons or winged sanitary towels, that seems obvious in hindsight. But, like all great ideas, it took someone to think it up, and that someone was James Campbell - a stand-up comedian who made a decent living, thank you very much, plying his trade before crowds of under-40s. Forget balloon elephants, revolving bow-ties and bunches of flowers whipped with a flourish from magic wands - Campbell shuffles on stage as laconic as any Comedy Store veteran and chats to the kids as equals; and, my God, don't they love him.
Campbell's audience is full of adults - all those kids didn't bring themselves - and his act is partly (and unashamedly) aimed at them, too. There is a children's connection when he tries to explain the meaning of irony to those who don't grasp it and who use phrases such as "social and political import". Certainly, the loudest laughter in the place came from a vast, bearded thirtysomething man sitting behind me. My own father, who is 71, enjoyed himself as well. I can make jokes about my dad not getting out much or about his mental age regressing toward that of an eight-year-old, but that would be unfair on the star of the show.
Campbell does have many stories about old people - including one about watching the bathwater drain away and thinking of one's life draining away - which my father took in good part. Most of all, he enjoyed the repartee that Campbell engaged in with the children in the audience. One particularly prissy child, who frequently interrupted when taking the surreal stories too literally, reminded him of Martin, the precocious child in The Simpsons. Looks like my father and children also share a taste in TV programmes.
Campbell has a difficult balancing act, and he carries it off well. So well, in fact, that his attempts to maintain a parallel adult career have apparently foundered on the rock of his persistent young fans turning up at grown-up gigs, squealing with laughter and making it impossible for him to swear or talk about sex. My own kids have been to see him many times before. In fact, they know several of his routines off by heart, just as my generation once parroted Monty Python sketches. They've recited Campbell's spiel about how sinister he finds the lyric "tiny tots with their eyes all a-glow" so many times now that I could muster a passable stab at reciting it myself.
So, what do kids actually laugh at? Well, don't expect any huge surprises. In the end, it's mainly funny faces, animal grunts, silly noises and the dreaded (guaranteed laughs every time) P-word: "pants". Campbell has only to mention pants to convulse the under-14s in his audience. But, to his credit, he does so only once, with a word of apology to the adults present.
There are surreal flights of fancy - going to school by catapult, attached to one's front door by an elastic rope, then simply letting go of the desk at home time - and a smattering of old jokes. "It's like Piccadilly Circus out there," he says, describing the traffic outside the Criterion Theatre (copyright 1825). Dealing with child hecklers is trickier than handling their grown-up counterparts, as the comedian's standard repertoire of put-downs is hardly applicable. Instead, Campbell drifts into teacher territory when a party of latecomers shuffles in. "What part of two o'clock didn't you understand?" he says. Convulsive high-pitched shrieks fill the theatre again - kids love teacher wit.
Personally - and I don't think it's just because I'm a comedy producer by trade - I found the mechanics of adapting the stand-up's art for children one of the most fascinating aspects of the show. A consistently high pace is required - it's not unusual for an audience member to be hysterical with laughter one minute, then fast asleep the next, and any momentum tends to be short-lived. But equally, a kids' stand-up cannot afford to overcook his audience: if he takes them to too high a pitch, they get all silly and out of control. So Campbell has to rein himself in and bringing down the pace - just for a moment - at regular intervals throughout.
For grown-ups, the children in the audience were probably the best part of the show - especially the know-alls. "If you went to school by catapult, you'd bang your head on a wall," announces one extremely confident, serious-minded and logical eight-year-old in a loud voice.
"Yes, I know," Campbell retorts. "That's why the image is funny." The adults laugh at the unforgiving nature of the put-down, and the kids laugh at the funny face he pulls while saying it.
At one point, he enquires of another boy what his favourite kind of towel is. "Barn," the child replies, in all seriousness. That sends Campbell into hysterics - and a five-minute ad lib about a towel that goes "to-whit-to-woo".
Campbell's readiness to go off at an improvised tangent is one of the more laudable aspects of his act. My children tell me delightedly of an incident at a previous gig when one child, unable to hold himself in any longer, marched off to the loo for a wee. The minute he was out of the door, Campbell marched the audience on stage and made them hide behind the curtains on either side. When the small child returned, Campbell was still performing but the audience had apparently vanished.
He also has an entire Spider-Man routine, based on the spider-bite that turned Peter Parker into a superhero, which begins with the question: "Has anyone here ever been bitten by an animal?" Whatever the answer, he has to improvise the rest accordingly. On the afternoon of our visit, the response was "an ant". Cue a pretty decent improvisation about a superhero with magic powers who could always be beaten by a villain brandishing a kettle of boiling water.
With TV slow to act on a performer who doesn't fit into any of its pre-existing categories, and the Criterion's first afternoon opening only two-thirds full, only time will tell whether Campbell proves to be a false prophet or the beginning of a whole new movement.
'James Campbell's Comedy 4 Kids', Criterion Theatre, London W1V (0870 534 4444) to 8 January. Harry Thompson is a television producer whose credits include 'Have I Got News for You', 'They Think It's All Over' and 'Monkey Dust', of which a new series begins on BBC3 on 4 JanuaryReuse content