Wiggles: How did four ageing Australian musicians become the world's bestselling pre-school act?

In the necessarily virtuous world of your typical children's entertainer, the Wiggles' Anthony Field, a man whose teeth dazzle like Simon Cowell's, has just one skeleton in his closet. But it's a good one. Long before the 47-year-old became an integral member of the world's biggest pre-school act, he knew his way around an Uzi.

"For some reason I'd signed up to the Australian Army, perhaps convinced that my experience was going to be like Elvis's in GI Blues," says this blue-eyed man child with a smile so bright it lightens up this atmospheric London hotel bar like electricity. "I did get sent to Germany [as Elvis did in the film], but that's where the similarities ended." This was, he adds, pre-1989, and the Wall had yet to crumble. Field's job was to patrol the border, machine gun in hand, all the while trying to hide his true feelings of abject terror.

"I kept thinking to myself, What the f... , I mean, how the hell did I end up here?" He laughs. "So I quit, quickly, and went home." Before the army, Sydney-born Field had had a musical career. He and Jeff Fatt, a now 56-year-old Australian of Chinese origin, spent a decade in a rock band called the Cockroaches. But by the end of the Eighties, The Cockroaches were on their last legs, and so when a mutual friend, Murray Cook, a part-time taxation officer who had also been studying early childhood education, suggested they try writing an album for children, they enrolled another friend, Greg Page, and the Wiggles were born.

"The record label said we'd be lucky to sell 3,000 copies, but we shifted over 100,000," says Cook, a 49-year-old human version of Bungle from the Seventies TV kids' show Rainbow: bear-like and cuddly, and with a perennially dreamy smile on his face. "We've not really looked back since."

Two decades on, and to a world of five-year-olds (and a great many of their approving parents), the Wiggles are superstars, their day-glo, nursery rhyme-like songs the sound track to any self-respecting toddler's life. They have sold more than 20m CDs and DVDs worldwide, and in 2005 were certified Australia's biggest export. A year later, they sold out out New York's Madison Square Gardens 12 times over (Coldplay, in comparison, managed three). Today, the Wiggles is an ever-mushrooming brand, with merchandise, a globally syndicated TV show, and, in Australia, a theme park. They are worth £25m, but unimaginable wealth has done little to staunch their rampant ambition. They still play upwards of 200 shows a year.

In the UK this month for their biggest tour to date, their first stop is London's tiny Garage venue later this afternoon, before an audience of competition winners and, in one corner, the actor Simon Pegg, his wife, and their one-year-old daughter. "There is something so beguiling and uplifting about their uncynical commitment to making children happy," Pegg says. "Behind all the crazy songs and colour, there are brains and heart."

Up on stage, the quartet – flanked by regular co-stars Captain Feathersword, the friendly pirate, and Dorothy the Dinosaur – lead some excitable tiny tots in a succession of happy-clappy song-and-dance routines, each lasting no more than two minutes. The mood is inclusive, and silly, and fun. The band never once stop smiling – no small feat for performers condemned to repeat lyrics like "Toot toot, chugga chugga, big red car" (from Big Red Car) hundreds of times a year, when they could, quite frankly, be off playing golf instead. Do they never tire of it all? "Not really, no," Cook insists afterwards, still beaming. "It's the kids, basically. They are a wonderful audience, and they remind us what a wonderful way this is to make a living."

And so what, precisely, is the secret of their such broad appeal? In a nutshell, they do what they do very well indeed, and their songs are genuinely catchy and funny – a crucial factor which helps diminish, if not entirely eradicate, the irritation levels for those poor parents sat alongside their children watching the DVDs on an endless loop.

"Our main inspiration is Sesame Street," says Field, who when not in costume wears a lycra T-shirt that reveals a pair of bulging biceps covered in tattoos. "And it would be nice to think that, like Sesame Street, the Wiggles can continue forever." Perhaps they will. They have recently gone into franchise, which means there is now a Taiwanese Wiggles and also a Latin American one, with more planned. And even their own line-up has survived upheaval. In 2006, founding member Greg Page was forced to retire after being diagnosed with a strength-sapping illness. He was seamlessly replaced by Sam Moran, 32, previously a Wiggles understudy. And Moran is not the only understudy. More are waiting in the wings.

"But there are no plans for us to retire just yet," smiles Fatt, a man now within touching distance of 60. "We may not be as young as we once were, but we do keep fit."

He and Field, he explains, are enthusiastic cyclists, while a massage therapist accompanies the tour to deal with all the dodgy knees and bad backs that come from a lifetime of on-stage handstands. "We lead pretty disciplined lifestyles, which also helps," Field says, adding, perhaps unnecessarily, that they employ, as a rule, a "zero tolerance to drugs".

Have any of them, I ask, ever played a show hung over? His reply is deadly serious. "That will never happen." Back at the Garage, and shortly before the climactic Hot Potato ("Hot potato/mashed banana/cold spaghetti" ad infinitum), Simon Pegg and family make a discreet early departure. His was the only famous face here today, unusual for Wiggles shows, which are invariably full of them. Recent wanglers of tickets – and backstage passes – include Chris Rock, Jerry Seinfeld, Sarah Jessica Parker and Metallica.

"Robert De Niro too," Moran adds, proudly.

De Niro came to see them at a show in New York. Moments before they were due on stage, they had a call from the actor's manager to say "Bobby" was running late. Could they possibly delay going on until he arrived? "And you know what? We actually contemplated it!" Field says, laughing.

Ultimately, however, they decided they couldn't. There were, after all, thousands of children out front already anxiously expecting them, and the Wiggles are nothing if not respectful of their audiences.

De Niro ended up missing the first half- hour. He dealt with it.

The Wiggles' UK tour runs until 4 July. For more details see Thewiggles.com.au

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