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Anyone who has been stopped by a small teenager with a big gun at a roadblock in Africa will tell you that it is all too easy to forget that the person in front of you – often wildly pop-eyed with drugs – is a child. But take the gun away, remove them from the guerrilla army and put them back in the classroom and they will produce drawings which all too readily bring home their age.

The drawings on these pages have been assembled by a number of charities that rescue child soldiers and try to restore to them the childhood of which war has cheated them. It is estimated that today some 300,000 children – between the ages of 7 and 17 – are involved in more than 30 conflicts worldwide. Abducted boys are forced to become combatants and girls to become domestic labourers and sex slaves.

The Independent's Christmas Appeal this year is asking readers to donate to the work of Unicef in the Central African Republic where it has an extensive programme to negotiate with rebel groups to get these children freed. It runs transit centres where children who have been released are demobilised, put back in school, given psychological help and vocational training, and reunited with their families or resettled with foster carers. To do this work Unicef relies entirely on donations from the general public.

"You cannot recapture a lost childhood, for the innocence has gone," says Dr Rachel Calam, who is Professor of Child and Family Psychology at the University of Manchester. "But you can offer a stable and secure background in which these children can experience kindness as the normal adult behaviour rather than violence and aggression."

Dr Calam first came into contact with the psychological problems of child soldiers a decade ago in Uganda, when she ran a workshop on post-traumatic stress at Makere University in Kampala for Ugandan psychologists who had been working with rescued child combatants.

"Childhood is a process whereby the individual gradually becomes more independent, and learns how to cope with life and form long-lasting relationships," she says. "For these children all their experience of these educational, social and intimate relationships has been distorted. They have undergone initiations to dehumanise them, being made to kill other children or their own parents. Those who can't keep up on forced marches are killed. It is done so that they know they will never be able to return to their home villages, to make them feel dependent on the militia and to terrorise them into compliance.

"So it's really important for children after they are rescued to be put in a context where they feel safe and secure. Where they can have the conversations that these drawings prompt."

What the drawings – gathered by Unicef, World Vision, Red Barnet, Gusco and AVSI and the International Rescue Committee – show is ex-child soldiers trying to come to terms with the horrifying events they have experienced, witnessed or perpetrated.

"Drawing can serve a lot of functions," says Dr Calam, who makes comments on the individual drawings in the captions here. "It helps the child to process what has happened to them. There'll be disconnects because of the strategies they have developed for coping; they may be very mature in some ways and immature in others. Aggression will be very common."

The pictures show that in a jumbled mix of power and powerlessness, cruelty and helplessness, anger and pleading, guilt and terror. "These children will carry this with them into adulthood," says Dr Calam. "By drawing it they attempt to gain control over it".