A 12-year-old girl from St Helens has been shot by police with a Taser electric stun gun, an investigation has found.
The schoolgirl is one of more than 20 young children hit with the weapons despite concerns they can lead to fatal heart attacks.
They include six children aged only 14, four youngsters aged 15, and 13 teenagers aged 16. Scores of other children as young as 11 have been threatened by officers with the weapons.
Young people's charities and human rights organisations said the use of Tasers on young children was deeply worrying. They said the high-powered weapons - increasingly in use across Britain's police forces - should only be fired on children as a last resort.
Amnesty International's Oliver Sprague said: "These dangerous weapons should not be used against children in all but the most exceptional circumstances. And only where there is no alternative to prevent loss of life or in genuine life-threatening situations.
"In the United States more than 500 people have died after being shocked by a Taser and, in many instances, the coroner declared the Taser as the contributory factor.
The investigation found Merseyside Police shot the 12-year-old girl in St Helens as she brandished two knives and threatened to harm herself.
A spokesperson for Merseyside Police, which shot the 12-year-old schoolgirl, said: "Officers were called to an incident in St Helens, where a 12-year-old girl, who was armed with two knives in a public place, was threatening to harm herself and behaving aggressively towards the police.
"Officers instigated the normal post-incident procedures to determine the full circumstances of Taser deployment and found that it was fired in line with force guidelines, as a proportionate and appropriate method to deal with the situation."
In total, at least 194 children aged 16 or under have had Tasers deployed on them in the last three years, according to the figures uncovered by investigative agency OpenWorld News under the Freedom of Information Act.
It includes at least 24 shot with Tasers - where the officer pulls the trigger shooting out a pointed barb attached by a wire to deliver an electric shock.
Another 97 children were 'red dotted' - a particularly threatening gesture by officers pointing the Taser at the child pinpointing exactly where the barbs will hit their body with a red 'sniper's' dot.
This included two 11-year-olds in the same location in Crewe allegedly armed with knives.Two 12-year-olds were also red-dotted, including a schoolgirl in Ellesmere Port who was carrying a knife, and another by Lancashire Police.The use of the stun weapons against young children comes despite advice to the Home Office that Tasers are more likely to cause heart problems in children.
The advice, from independent scientific body Defence Sub-committee on the Medical Implications of Less-Lethal Weapons (DOMILL), was published in the Association of Chief Police Officers (ACPO) Taser guidelines.
It notes "children and adults of smaller stature as being at potentially greater risk from the cardiac effects of Taser currents than normal adults of average or larger stature".
A total of 27 forces provided detailed responses on the use of Tasers against children, including an age breakdown, during 2010, 2011 and 2012.
It means the true figure of Taser use on young children is likely to be much higher as a number of forces, including London's Metropolitan Police force, have either delayed providing a response, or refused outright.
Tasers are increasingly being carried by police on Britain's streets after first being introduced in 2004. After a trial of five forces across the country it was decided that the weapons should be made available to all constabularies throughout England and Wales.
At the time, only authorised firearm offices were allowed to use Taser but this changed in December 2008 when use was extended to specially trained units.