Professor Kumquat, in specs and a lab coat, solemnly takes his place before the Scottish Parliament's transport, infrastructure and climate change committee. He sits cross-legged on the floor, but no-one seems to mind. The chairwoman, Jamila, 14, looks briefly at her notes then invites him to submit his idea.

"I believe that those who throw away food waste should be given two weeks in prison," he announces. Though this will almost certainly lead to a large increase in the prison population, he concedes, it will be a straightforward matter to build more prisons - out of old tyres.

A voice pipes up from the left. It's the SNP MSP, Ben, 10, and he's frowning. "But how would you know that a particular person had thrown away certain stuff?" he asks, fixing Kumquat with piercing eyes. This is greeted with a murmur of agreement and nodding heads: good question. Prof Kumquat, however, is unfazed. "Suspicious compost would be sent away for fingerprint analysis," he says. Laughter and exclamations of disbelief temporarily drown out the chairwoman's counter question: surely it would be better to have some sort of fine instead? "We could look at that," agrees Professor Kumquat, with a slightly injured air.

Further questions are fired in from all corners of the floor: the mood of the committee is bullish and Kumquat is looking increasingly isolated. Then the bell sounds and it's time to vote. Madam chairwoman turns briskly to the committee and asks them to vote on the question of fining people who don't recycle. Everyone raises their hands in agreement and the defeated Prof Kumquat - aka volunteer Mick Blunt - retires to lick his wounds.

If it were a real committee of the Scottish Parliament, it would be the best attended, and best reported, of them all. As a role-playing game for 10- to 15-year-olds on a residential weekend in Fife, part of the ground-breaking Children's Climate Change Project, it's a bit of a laugh, but also a chance to do some serious thinking about the environment. The children, who have been randomly assigned their roles as MSPs and witnesses, have lots to say. Next comes a proposal from 10-year-old Laike that wind turbines should be painted cool colours (unanimously agreed) and another well-argued submission from 10-year-old Paddy to limit the amount of petrol a person can buy in a week, which leads to a discussion about workability (Labour MSP Caitlin, 10, wants to know what would happen if you broke down on the way home). Just the sort of issues, in other words, that you would expect to hear MSPs tussling with on a real committee.

But then the whole point of this project, a collaboration between World Wide Fund for Nature (WWF), Children in Scotland and the Children's Parliament, is to demonstrate that children can make a considered contribution to serious political debates. With the Scottish Parliament due to consider the Climate Change (Scotland) Bill this year, the project has been set up to allow children to feed in their views. Jess Pepper, WWF Scotland's parliamentary officer, who came up with the idea, says: "These guys have the biggest stake in what we do or don't do now on climate change." The project kicked off on Friday with the residential weekend for 20 children at the Ecology Centre at Kinghorn in Fife, a place for children and adults to experience the natural world first hand. Then in August, during the Festival of Politics, the children will present their conclusions at a Scottish Parliament event. Later in the year, when the Bill is being considered in committee, the children will submit written evidence and may also be invited to give oral evidence. It is the first time children have been involved in the legislative process while a bill is being drafted, on any issue. "We are leading the way in the UK in taking children's involvement seriously," says Paula Evans of Children in Scotland.

The suits and soundbites of the Scottish Parliament seem a long way from the Ecology Centre which, on a lazy Sunday afternoon in June, is about as close as you could get to green heaven. A jumble of terracotta-roofed farm buildings sit on the hillside overlooking little Kinghorn Loch, which lies in a tree-lined basin. Children are bounding up and down between workshops in a converted barn on the hill and the famous Earthship down below, a fully sustainable house made of earth, sheep's wool and recycled tyres and cans. In a marquee on the grass in front of it, the children are working on a mural to be unveiled at the Festival of Politics, and next to it are four large yurts strewn with rugs and sleeping bags, where they have been sleeping. They have come to the project from Children's Parliament groups in Edinburgh, Ayrshire, Fife and the Western Isles, and come from a whole variety of different backgrounds. Under the hot June sun, though, everyone is equal.

Ideas are coming thick and fast. Jamie, 15, from Barra, who has seen Al Gore's film An Inconvenient Truth and read books on climate, emerges from the activists' workshop with an idea for a publicity stunt to highlight the problem of aviation emissions: go into parliament and every time the minister stands up to speak, play audio of an aeroplane landing. Luckily for John Swinney, a keen supporter of the Climate Change Project, it's just an exercise in creative thinking, not a serious plan. He's more interested in presenting the children's ideas to MSPs at the Festival of Politics. "The Children's Parliament might influence the bill. I'm looking forward to that," he says.

During a break between workshops, I catch up with 10-year-olds Christie and Emma from Fife, who are chilling out by the herb garden. "I always knew climate change was a big issue. I didn't know litter gave off CO2, but I did know you had to walk rather than drive," says Christie. But she is not convinced by all the focus on Scotland's world-leading role. "When you say it's up to Scotland, I don't think it's up to Scotland. All I want is for the majority of the world to start doing something; America and Russia and England together."

"I thought America would be at the front," says Emma.

Didn't we all.

Beyond passing on the information the children need to understand the issues, always from a range of perspectives, the adults have kept their own views out of it. "They are not being told climate change is bad because of this and this'," says Cathy McCulloch, co-director of the Scottish Children's Parliament. "On the issue of nuclear power stations, for instance, you'll have one child saying, we'd better give it a try, while others will say, no, it's really dangerous and if it blows up we'll all die."

The Children's Parliament is emphatically not an organisation for a self-selecting group of the brightest and most articulate children, but for all children. At least half of its participants are from what McCulloch describes as "difficult backgrounds".

"The Children's Parliament is about saying children are not citizens of the future, they are citizens now," says McCulloch. The adults just act as mediators, helping the children feel confident enough to speak to MPs, councillors or other prominent adults, by themselves.

Morag Watson, meanwhile, WWF's education policy officer, has been struck by the change in the children over the course of the weekend. "One of the girls put her hand up on the first day and said, Are we going to die?' When they first came they were so scared about what climate change meant for them. But they are so much more positive now."

As the day draws to a close, the children come together to talk about what will happen later in the summer. Jamie from Barra pipes up: "This is just like the G8 summit, except for younger people." Scottish Parliament, watch out.

Going Green
Emma, 10, from Fife: In the next few years, the oil's going to run out. It makes me really worried because I'm not going to be able to fuel my car or get heat for my house.

I'd like to live in an Earthship.

Lorraine, 10, from Edinburgh: The polar bear could become extinct and one billion people depend on polar ice-caps to live. Before this, I never composted, but when I go home I'll do lots of composting.

Samantha, 10, Edinburgh: I'd like to see the government do more. It hasn't put emissions from planes in the bill.

Sarah, 13, from the Western Isles: I knew climate change was affecting lots of different places and was creating extreme weather. I'll stop leaving my iPod on accidentally.

Connor, 14, from Ayrshire: Last year I saw a humming bird hawk moth and they only live in warm places. It's mostly when you go over to Spain and France that you see them. The fact that you see them coming up here is a big thing. There are lot of different views on climate change and some people say we have already done so much but it's going to happen anyway. Then there are people who say, we have to do everything we can. Which camp am I in? I'd prefer to be in the latter but there's always a part of you that says you can't change what's been done in the past.