The more time they spend away from home, travelling the world playing to packed houses and mingling with celebrities, the less the Kings Of Leon's roots show. Especially now that all but one of them has ditched the shaggy look that made them easy to pick out of a crowd when they arrived on the scene a couple of years ago.

So it falls on us to look a little closer for the peculiarities that still set the youthful Tennesseans apart from their peers - like the uncharacteristically wholesome way they've blanked out expletives (and there are more than a few) in the lyrics provided on the liner notes of their much buzzed-about second album, Aha Shake Heartbreak.

Guitarist Matthew Followill, fielding questions in Toronto this week the day before a sold-out gig at the Opera House, looks perplexed when confronted with this eccentricity. But then, he would. While he shares the same last name as singer Caleb, drummer Nathan and bassist Jared, he's only a first cousin to the three brothers - meaning he's slightly out of the loop when it comes to family connections.

It falls on Jared, at 18 the baby of the group, to intervene. "That's for our mom," he explains, offering that hearing her boys use "the c-word" (and, it seems, several other words) makes her cry.

If that's the only concession they have to make to their conservative background, the Kings should count themselves lucky. After all, as has been widely reported, their journey to a life of sex, drugs and rock 'n' roll (with a heavy emphasis, legend has it, on the first two) has been a most unusual one.

On the road with their father, a travelling Pentecostal preacher, the three Followill brothers barely listened to rock music, let alone played it. But after their dad got out of the preaching business and they wound up stationary in Nashville, Caleb and Nathan somehow took to songwriting.

One thing led to another, and they found themselves facing the prospect of a major label deal - provided they could fill out their lineup.

Jared, then 15, was dispatched to buy a bass and given a month to learn to play. As for Matthew, he'd at least had a brief flirtation with the guitar before giving it up at 14. So when he got the call from his cousins, he opted to ditch his grade 11 classes, run away from home and relearn his licks.

The results were inevitably rough. "It was really quick," Matthew recalls. "I had to learn five songs in two weeks. And then the head guys from RCA are sitting in our garage ... Caleb breaks a string and it takes him 30 minutes to change the string because nobody really knows how."

That the Followills were so rough around the edges proved a help rather than a hindrance, though, when it came to winning over fans - particularly in England, where it lent them an exotic quality that helped debut album Youth and Young Manhood go platinum. "We thought people wouldn't like our story," Matthew says. "But they immediately loved it."

Now approaching similar success stateside, and set to begin a stint opening for U2 on its forthcoming North American tour, there's no question the Kings have evolved considerably - and they know it. "The first album we were just kids," Matthew says. "Then we just toured for so long that we progressed on our instruments.

"Being on the road and seeing the world is like going to school. It makes you smarter and more confident. So I guess it all kinda shows on the second record."

That's not an unduly generous assessment: Aha Shake Heartbreak is indeed a major leap forward. Caleb's endearingly swampy vocals are still there, which helps obscure lyrics that haven't progressed as quickly as the music. But the band's sound is tighter, peppier and more distinct than on its debut, which renders critics' ceaseless Strokes comparisons lazier than ever.

Live, the Kings have come even further. Always better on stage than in the studio, their punchy hour-long Toronto set was one long adrenaline rush. And with the band seamlessly splitting the set list between their two albums, the older offerings stood up well enough to prove how well they've been road-tested.

There's still room to grow, of course. Enjoyably compact though their show was, there's room for taking a few more liberties - as they did closing their main set with a glorious rendition of Youth and Young Manhood's Tranny, allowing their guitarist to demonstrate how much he's learned on the job.

With every gig, though, they seem to be coming closer to the perfect fusion of garage rock professionalism and the southern-fried charms they've made their name on. They still look and sound like boys from Tennessee - just less like ones who've never left the state.

And yes, their family is now good with it. "We go to family reunions and there are people I've never even met before who are hugging me and kissing me," Matthew says . And why wouldn't they? It's not every day that a few sons (and one nephew) of a preacher man strike rock 'n' roll gold - and still remember that it's not nice to make their mama cry.