Laura-Anne Hanrahan is sitting on her doorstep, playing with a pumpkin as she describes how she felt when her boyfriend kissed her.

'Tingly,' she says, dreamily. 'He used to come over and cuddle me and put his hands up my top. It used to feel cosy. I feel desperate to go up to him and say "Ben, why don't we kiss any more". It hurts so much that we don't kiss that I want to rip my heart out and throw it away.'

Laura-Anne, from Siddick, a two-street village near Workington in Cumbria, is nine years old.

Next year she will become a star as the main character in a fly-on-the-wall documentary about the sexual awakening of Britain's pre-teens, with her every thought pored over by television critics and sociologists. The makers of How To Fall In Love, due for broadcast by Channel 4 in the new year, spent two years following the primary school pupil and her friends as they discovered the opposite sex.

The Observer has seen the film. To some it will be a sweet and tender portrayal of childhood love, while others will rage against the increasingly sexualised world in which children grow up.

Laura-Anne is shown massaging 11-year-old Steven Hilland while he watches TV and eats crisps. Asked later about the scene, she tilts her head coquettishly and says: 'Sometimes I dig my nails in and scratch him hard.'

'I love it when you do that,' Steven replies with a grin.

In another scene, a heartbroken Laura-Anne shakes her head in disbelief as she reads a 'Dear John' letter penned by her 'first love'. 'It is hard for me to write this letter,' states Ben Challenger, aged 10. 'But I think we should have some time apart, because Steven is forcing me to go out with you and it doesn't feel right.'

In one of the most contentious scenes, two 10-year-olds are seen energetically participating in the kind of kissing normally undertaken behind the school bike shed. It has prompted a debate about the ethics of using potentially vulnerable children as documentary subjects, with one parent saying he felt that his son had been 'exploited and manipulated'.

'I'm not suggesting he was made to do anything he didn't want to do,' Steven Hilland said about his son, also Steven. 'But he was definitely encouraged by promises of burgers, go-karting and ice-skating. He didn't want to have a full-on snog with his girlfriend in front of the cameras, but he said he was persuaded to, and now he is embarrassed about everyone seeing it.'

Marc Isaacs, the acclaimed director of the film, admitted that some of the scenes, including the one Hilland mentioned, involved 'set up' shots, but insisted it was an accurate portrayal of what he witnessed during the two years he spent following the children. 'At first they were very excited, but then quickly got bored of the filming,' said Isaacs, who won the Grierson directorial award for best newcomer in 2002.

'We spent two years with them, because I didn't want this to be a surface portrait - so of course we took them to the pictures and bought them lunch and gave them Christmas and birthday presents. We did intervene and create scenes, but all the things that happened are completely true.'

Siddick, where the documentary was shot, is surrounded on one side by an enormous paper factory and on the other by a row of wind turbines. Visitors are welcomed by signs reading 'Please Die Carefully'. Once a busy mining area, it is now plagued with high unemployment. Despite this, there is a palpable sense of trust and community. Doors are left unlocked and children play outside until late in the evening. Now there is much talk about the impact the film, to be shown at a special screening in the local cinema on Tuesday, might have on the village and its residents.

Laura-Anne, who is now 11, Ben, 12, and Steven, 13, have mixed feelings. 'Most people my age think about boys and falling in love all the time,' said Laura-Anne. 'It is good to make a film about it rather than pretend it doesn't happen.'

'You have to have a girlfriend,' said Ben. 'Otherwise you just get wound up and people think you're not attractive.'

Although the programme is not sexually explicit, Steven told The Observer he first had full sex when he was 11, and had been several times to the family planning clinic. All the children said they had their first 'proper kiss with tongues' when they were six or seven.

This month The Observer revealed plans to introduce compulsory sex lessons for primary school children as young as five. Although the government later distanced itself from the report, which sparked fury among some church groups, there is growing support for sex education to begin much earlier.

Janice Hanrahan, Laura-Anne's mother, said: 'It can be very uncomfortable to see your nine-year-old on TV talking about being in love but it actually reminded me of having those feelings at a similar age. You simply forget as you grow up.

'People who say they want to keep children safe and innocent for as long as they can are fooling themselves. If children are not given sex education at home or in school, they will gather their impressions anywhere and everywhere: from explicit prime-time television jokes, soaps, magazines and the net.'

While many parents will be horrified at the thought of their pre-pubescent children engaging in any kind of sexual activity, some experts argue that we are all sexual beings, that children learn about touch and loving relationships from day one and that parents need to be comfortable talking about sexuality with their children early on.

Others expressed concern about a film showing nine-year-olds as sexually curious. 'There is already so much pressure on children to grow up,' said Mallory Hensen, a senior educational psychologist with Milton Keynes council.

'We hear about young girls wearing Playboy T-shirts and G-strings. We are already sexualising children far too much and treating them as young adults.'