First Night: Underage Festival, Victoria Park, London

At first it feels like we're back at school. At the official start time of midday, no one has been let in yet and thousands of teenagers are lined up in separate queues for boys and girls, clutching tickets printed out off the internet.

It's billed as "the world's first credible festival for strictly under-18s" but everywhere I look there are groups of grown-up reporters and cameramen tracking our every move. And that's before we reach the security men, checking our ages (only 14 to 17s please!) and our bags for fags and drugs and booze - because this is also Britain's first alcohol- free festival.

Underage might be run by teenagers but the adults are definitely still in charge - including the sponsors who hand out branded badges, stickers and - hel-looo?! - cigarette lighters!

We're eventually let in, one by one, through security that seems a lot stricter than a normal festival. Do they make you stand in straight lines and separate the sexes at Glastonbury?

Early on, Lethal Bizzle - a lone rapper on an indie-heavy line-up - gets a big response from the Nu Ravers but the poor Errorplains, playing to a half-empty tent with half their fans queueing outside, confessed they probably knew the names of their entire audience.

Once the place began to fill up, you got a picture of the crowd: boys in skinny jeans, band T-shirts and big sunglasses, and girls in ... well, the same, really, or strapless summer dresses and footless tights. Then there were the ones in fancy dress - fairy wings, Hawaiian flower garlands, animal ears and top hats with face paint and ink on their faces and bodies.

The strangest thing by far, though, was that despite a line-up of almost 40 bands, including hot indie names like Cajun Dance Party, The Mystery Jets and Jack Penate, the majority of people sat around the park in small groups with their friends, chatting, texting, and even listening to iPods. It seemed the main attraction was not so much the music as the chance to get together with your friends without adult interference.

At times, the fact it was an under-18 festival added to the atmosphere, with plenty of fans playing Frisbee and flying kites, while Cajun Dance Party brought the mood onstage, throwing balloons into the crowd.

But every so often you got reminded of the downside of being underage: like when The Teenagers began their best-known tune, "Homecoming". The French band had prepared the "highlight of their show" to be bringing up a girl onstage to sing the female vocals in their most risqué song. Unfortunately, no sooner was she picked and ready to climb over the barriers, to the cheers of the excited crowd, than the security men stepped in and told her to get back down, saying that no one was allowed onstage with the band.

Who was best? The Pigeon Detectives, Cajun Dance Party, The Mystery Jets and Jack Penate all got good feedback. My favourites? Definitely my school friends Pull In Emergency - remember the name!

So overall: we had sunshine, we hung out with our friends, we got to see loads of our favourite bands for £20, and we did it all without any adults (apart from the security men, the reporters, the photographers and the PR people). And we got to stay up 'til The Young Knives brought the day to a riotous close ... at 8pm.