Parent groups and religious organisations have discovered something more reprehensible than rap music on U.S. airwaves – it’s a TV cartoon show which focuses on foul- mouthed children telling dirty jokes.

The animated show is ‘South Park’ airing on cable television’s Comedy Central and – despite a growing wave of opposition from groups who find its contents offensive – it has proved one of the biggest trends in recent years as to what’s ‘hip’ with teenagers.

Since the show first aired last year, its characters have appeared everywhere from T-shirts and stickers in most shopping malls to the covers of ‘Newsweek’ and ‘Rolling Stone’ magazines.

It is also a bona fide controversy, eliciting a constant stream of opposition which has required Comedy Central to label it ‘TV- MA’ (or for mature audiences only) – an inauspicious first for a cartoon show whose primary audience consists mainly of teenagers.

The animated show’s creators and lead voices, Trey Parker and Matt Stone, have become overnight stars, appearing in the new Jerry Zucker-directed movie ‘Baseketball’ and working on an upcoming film of their own called, predictably, ‘Orgazmo’.

The peculiar thing behind the ‘South Park’ sensation is the relatively modest, if funny, premise of the comedy itself. The show depicts the “everyday life” life of four children from South Park, Colorado, and their bemused reactions to the bizarre events around them – including mishaps that inevitably result in the death of one of the boys, the inarticulate Kenny.

In a regular twist typical of the show’s humour, Kenny always tends to be killed in strange ways – becoming impaled on a flagpole, or pecked to death by rampaging turkeys – which prompt his friends, Kyle and Stan, to yell out, “Oh my god, they killed Kenny!”

The fourth child in the crew, the fat and obnoxious Eric Cartman, is also responsible for some of the catch phrases that have become instant cliches in the wake of show’s success, from his gargled yelp of “Kick-ass!” (ie, good) to his screaming description of himself as a “beefcake” (ie, handsome).

The rest of the cast is just as distinctive, and includes popular soul singer Isaac Hayes as the voice of Chef, head of the school cafeteria, who always responds to the children’s questions about life with ludicrously inappropriate songs about sex.

Perhaps the main source of the show’s appeal, however, is the way the kids accept with a straight face all the genuinely bizarre, and often spectacularly gross, oddities around them.

In one Christmas-themed episode, Kyle, who is Jewish, deplores the fact he can’t celebrate Christmas like the other South Park kids – but cheers up when he is visited by a non-denominational visitor, Mr Hankie the Christmas Poo – a talking piece of feces who explains the meaning of the holiday while sullying every spot on which he hops.

In other episodes, aliens plant a giant probe in Cartman’s anus; Stan comes to terms with his dog’s homosexuality by travelling on a cruise called Big Gay Al’s Big Gay Boatride; and – in a self-referential moment – the South Park parents try to ban a vulgar television show, even as they joke about an epidemic of diarrhea going through the town.

A little of ‘South Park’ goes a long way; between the anything- goes obscenities of the plot and dialogue and the crudely-drawn, collage-style animation, the show is several degrees below even the MTV-spawned ‘Beavis and Butthead’ in its level of civilisation.

So far, Stone and Parker – who claim their childhoods inspired the characters of Kyle and Stan, respectively – have been content to parcel out a little ‘South Park’ at a time, from an initial run of a dozen episodes last year to a fresh batch now. But the show’s popularity is increasingly raising its two creators’ profiles, with plans for them to do more live-action films and even a ‘South Park’ movie.

Will the potty-mouthed show take to the big screen, or will the phenomenon die down once people get tired of the same flatulence jokes every week? Trying to keep the show’s simple premise fresh may become as challenging to Stone and Parker as any battles over its content have been.