In the summer of 1945, a Holocaust survivor called Willy Groag arrived in Prague with two suitcases full of paintings. They had been produced in Theresienstadt concentration camp, in Nazi-occupied Czechoslovakia, by children who were subsequently killed in Auschwitz. These works are usually on permanent display at the Jewish Museum in Prague, but now, for the first time, some of them have travelled to Britain to make up a show that says more about the Shoah than any work of art by an adult.
Around 15,000 Jewish children were imprisoned in Theresienstadt. With them were 45,000 adult Jews, including a Viennese artist called Friedl Dicker-Brandeis. This artist was a product of the German-Jewish liberal culture that flourished in central Europe before the war. She had studied at the Bauhaus. She spoke only German, not Czech. Nevertheless, in Theresienstadt, she set about teaching art to children in the same way that she'd been taught at the Bauhaus - showing them the vitality of colour and texture, and the value of careful observation. She organised competitions and exhibitions. In particular, she taught children to paint each other's portraits. In an environment where names had been replaced by numbers, this became the most popular genre for children and adults alike.
Before the war, Dicker-Brandeis had been a portrait painter, as well as a designer and landscape artist, but in Theresienstadt she did hardly any painting of her own. She saved her scant art materials for her pupils. And in doing so, she inspired a body of work that rises above the time and place in which it was made. For some of her pupils, the value of her teaching was that it allowed them to construct a fantasy land far from the misery of their surroundings. For others, she provided a way of bearing witness to their captors' crimes. Above all, she proved that in extremis, when humans are stripped of their humanity, art is not a luxury but a necessity.
While many of the works in this exhibition are escapist, others are brutally realistic. On one wall, children dance in a summer meadow. On another, drawn in much the same style, there are scenes of execution and burial. The youngest of these artists was six years old - she was one of the few who survived. Another survivor became a professional artist in Prague, where she still works today.
"Friedl Dicker-Brandeis really encouraged the children to be free with their imaginations, not just to depict their world but to transcend it," says Susannah Alex-ander of the Jewish Museum in Camden, north London, which has mounted the show. Yet the artist never tried to steer the children's work in any particular direction. "To direct the sparks of children's inspiration, those sudden illuminations, is criminal! Why are adults in such a hurry to make children like themselves?" she de-manded. These simple paintings - whether of funfairs, animals or deportees under armed guard - are resolutely childlike, and it is this that gives them their authenticity.
Adult art is usually shackled to its own era. These pictures could have been painted yesterday. "These weren't children who were different," says Alexan-der. Nevertheless, under the tutelage of Dicker-Brandeis, they created some extraordinary works. Adult art is self-conscious, and the more harrowing the subject matter, the more self-conscious it becomes. Picasso spent a lifetime trying to rediscover how to paint with the spontaneity of a child.
Some of the paintings are records of daily life inside the camp - the dormitories, the kitchens, the towers and the gates. Others recall the world outside - the discrimination of the pre-war years ("Jews not welcome", reads a shop sign) and the transitory sanctuary of home: a woman feeds geese beside the village pond; a family sits down to dinner. When, in 1993, a selection of these pictures was displayed at the United States Holocaust Memorial Museum in Washington, DC, Vaclav Havel observed: "There is only a shadow of grief and anxiety in them. There is much more about dreams of spring, of flowers, butterflies, birds, and also a great longing to be happy and carefree."
These happy, carefree pictures reveal the insanity of the Final Solution far more effectively than any photograph could. "It's more personal," says Hedy Franks, a survivor of Theresienstadt who has lived in Britain since the 1940s. Alexander agrees. "This is the beauty of the exhibition. Had we not had these drawings, we would have a list of statistics - this is the only way we would know about these children. Because of these drawings, because they survived, we can remember them as individuals - and honour them as real people." Alexander adds that remaining human in such inhuman circumstances was a sort of resistance, too.
It wasn't only children who resisted in this way, but adults as well. "There were some amazing painters and musicians, fantastic singers and composers," remembers Dorit Trant, another Theresienstadt survivor. There was remarkable camaraderie among the inmates ("we shared everything we had"), yet there was also terrible insecurity. Each week there were eastbound transports, and each week could have been her turn. Tens of thousands died in Theresienstadt, but at least there was a chance of survival. "There was so much talent there. Most of them were sent to Auschwitz, and that was that," says Trant. "We were lucky to have stayed where we were." It is remarkable that any art came out of Theresienstadt. The lessons Dicker-Brandeis gave were clandestine (her covert classroom was an attic), her pupils studied surreptitiously and there were hardly any materials. She hoarded every sort of scrap paper - cardboard, wrapping paper, even paper bags.
This exhibition is a small sample of the art produced. There were more than 2,000 pictures in those suitcases, and these were merely the ones that she had managed to hide - behind door panels and under floorboards - and that the few survivors managed to retrieve. Raja Englanderova, a pupil of Dicker-Brandeis who was responsible for recovering many of the works, remembered her teacher as a tender, intelligent woman who created a fairy-tale netherworld where present hardships were forgotten.
Of the 15,000 children imprisoned at Theresienstadt, only a hundred or so survived. The rest were sent to Auschwitz, along with their teacher. Dicker-Brandeis could have saved her skin by emigrating to Palestine - unlike a lot of Jews, she was offered a visa. But as a committed communist and a dedicated anti-fascist, she believed she should stay in Europe, so she had taken Czech citizenship and remained in her adopted home town of Prague. At Theresienstadt, she refused the bread that other secret teachers received from inmates for their work. The handful of pupils who outlived her remember her as petite and patient, with short hair and big, soulful eyes.
"I Never Saw Another Butterfly: children's art from Theresienstadt" is at the Jewish Museum, London NW1 (020 7284 1997) until 20 June. For further information, visit www.jewishmuseum.org.uk