By BETH HALE

Last updated at 14:37 20 April 2008

A blonde-haired girl with her hands strapped into boxing gloves sobs at the side of the ring.

In another image her twin brother takes a direct hit to the face from a sparring partner.

Miah and Kian Flanagan are just five years old.

But already they are seasoned fighters, taking part in an alarmingly fast-growing 'sport' that pits children against other children in the terrifying public arena of the boxing ring.

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Five-year-old Miah's face crumples in tears as she fights in the ring

The opponents - some of them barely old enough to be at school - kick and punch in chilling scenes, while parents shout impassioned advice from the sidelines.

Incredibly parental 'advice' includes encouragement to "come on Princess, go forward, kick 'em, kick 'em."

Welcome to the world of child Thai boxing, one of the fastest growing martial arts in the UK with now over 500 registered clubs teaching this sport.

Children as young as four or five are becoming the latest recruits to organised fighting, where some people's attitude is: "If you're good enough to fight, you're old enough".

The chilling snapshot into a pastime that is legal is laid bare on a Cutting Edge documentary to be shown on Channel 4 later this week.

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'Just enjoy yourself, baby' shouts her father as little Miah sobs

In the strictly governed world of conventional boxing youngsters must be at least 11 to compete.

But in MuayThai boxing there is no such limit. There is also no requirement for protective headgear, despite regular blows to the skull.

Parents have to sign a disclaimer before a fight, relieving promoters of any blame should their children be injured as they compete - sometimes in front of paying adult audiences.

Miah and Kian Flanagan live with their father Darren, a quantity surveyor, and mother Lisa, a nail technician, in Wigan.

The twins were enrolled in boxing lessons at their local gym seven months ago. Mr Flanagan is so passionate about the sport that he has converted the spare room into a gym so he can give the twins extra tuition.

Mr Flanagan believes that the training will help his daughter take care of herself.

"If someone grabs Miah when she's 15 what do you think is going to happen? She knows all the defence moves," he said.

"If I'd never taught my kids Thai boxing how guilty would I feel. Anyway Miah loves it - she's like a ballet dancer with boxing gloves at the moment," he told the the News of the World.

But footage from the programme shows that Miah often cries before going into the ring and her Dad instructing "Come on baby just enjoy yourself" before later ordering her "stop this now".

"Every time she goes in that ring, there is always a worry she will start crying," said Mr Flanagan, who says he has told his daughter she can give up if she does not enjoy it.

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Children as young as five are forced to fight each other in the ring as their parents look on

Such is his determination for his children to succeed that he even alters her diet to 'bulk' her up if she faces an older opponent.

Meanwhile his wife coats her daughter with glittery make-up and hairspray before she enters the rings.

Another child featured is Thai Barlow, already a veteran fighter at 10 and named after his parents burning passion for Thai boxing.

His dad Mark is his trainer who runs his own gym and mother Maxine was herself a successful fighter. Both Thai and his 14-year-old sister, a double world champion, have followed their parents' love of the sport.

On top of school and homework, a normal week for Thai consists of running over 15 km, doing 400 sit ups, and at least 10 hours on the bags and sparring.

Mr Barlow will travel anywhere in the world, forking out thousands of pounds to get his son fight experience.

"My dream and his mum's dream is for him to win a stadium title," he said. "I don't know what his dream is… probably to play with his soldiers."

On March 28 Thai took part in his first cage brawl, fighting inside a 23ft metal cage in front of a huge crowd paying 335 a ticket.

His opponent was nine-year-old Connor Butler, from East London. Both were shouted on by their parents, but Thai eventually lost for only the third time in 59 fights.

Despite his youth, his victories apparently include two knockouts.

Today Conservative shadow minister for Sport and the Olympics Hugh Robertson, said he was alarmed by the fight scenes described.

"If children are so upset by the prospect of doing any sport that they burst into tears before they do it then I don't think they should be forced to take part.

"While I support martial arts and boxing as sport I don't think they are sports for children below the age of seven."

Cutting Edge: Strictly Baby Fight Club is on Channel 4 on Thursday at 9pm