How does an author make a subject as brutal as war appeal to a child? A new exhibition suggests young readers today get a less sanitised version of the horrors of warfare, says Sanchia Berg of BBC Radio 4's Today programme.
Some of the most famous children's works have been shaped by war, or at least its consequences.
In The Lion, the Witch and the Wardrobe, the Pevensie children are evacuated from London to escape the Blitz.
And more recently, Michael Morpurgo's War Horse tells the tale of a boy whose horse is shipped off to fight in France at the start of World War I. The book, published in 1982, has been adapted into a play and will be appearing on the big screen courtesy of Steven Spielberg.
But tackling the violence of the conflict itself throws up obvious difficulties for any author - how to bring such a destructive world into the innocent mind of a child.
The Imperial War Museum in London has a new exhibition, Once Upon a Wartime, which illustrates a shift in the way war has been depicted to young readers, and brings five novels to life.
The Silver Sword by Ian Serraillier was first published in 1956. It tells the story of four Polish children, three from one family, who are searching for their parents in the chaos of post-war Europe.
Although the reality of this time was brutal and rape was common, the book is not generally frightening for children, according to the author's daughter, Jane Serraillier.
"The violence is off-stage," she says. "The adults are kind."
In fact, she says, it was difficult to get the book published in the US because the Russian soldier is portrayed in such a positive light.
Serraillier had lost his own father at the age of six, and his daughter is convinced it was this which drove him to write the book.
She cites the writer Alison Lurie, who has pointed out that children's writers have often suffered some trauma - that their childhood is suddenly deeply interrupted and they're drawn to recreate the world lost.
The trauma for many British children during World War II was evacuation, being suddenly taken from their own homes and families and transported to strange places.
Nina Bawden was sent to Wales, separated even from her own brother. She used the experience to write Carrie's War - which is still very widely read by primary schoolchildren. Its vivid description, its powerful evocation of the perspective and emotions of the narrator Carrie, evacuated to Wales, impress young readers.
One 10-year-old boy said he read loads of books, but Carrie's War was the only one which really came to life for him. "It's like a movie in the cinema. I can see it in my head," he says.
Bernard Ashley's Little Soldier is about a former child soldier in Africa who comes to London in the 1990s. Ashley was also evacuated, attending 14 different schools. He's written novels set in that period, but this one has a more modern setting and tone.
A young African boy, Kaninda, sees his family massacred and the experience is relayed through flashbacks. "Kaninda saw his father and mother in their hot, blood-wet heap on the floor."
He becomes a child soldier, but is rescued by United Nations forces and arrives in London, only to find himself caught up in gang conflict.
Ashley recognises that the violence and trauma is described in far greater detail in his book than the others in the exhibition. But that, he explains, is because children's literature has changed.
"Between the time that Nina Bawden wrote Carrie's War and Little Soldier [was published] children's literature has moved. Thanks to some brilliant British publishing from the 1970s on, children's books have changed.
"We now have books that so much more reflect the society we live in. We understand now that children can cope with different sorts of descriptions that maybe once they were not thought able to cope with.
"I remember the furore about The Machine Gunners by Robert Westall because there are one or two words in there that an adult might say 'hey - this is a children's book! And it says bloody!' When you ask children about that, they hadn't noticed. But the adults had."
Geoff Fox, a consultant to the exhibition, remembers reading books and comics about war during the 1950s. "The children's books I used to read, we always won - often with a 'straight to the jaw'. Death, if it was there, was no different from a cowboy shooting an Indian, as we used to say."
Now, he says, death is described in detail. Subjects once considered taboo for children are now the topics of many books, even the Holocaust. The Final Journey by Gudrun Pausewang takes place almost entirely in a cattle truck with families going to Auschwitz, and spares the readers nothing, says Fox.
He says children are far more "acculturated" now to violence, through the films and television they watch, and the computer games they play. "What's important is to deal with it in a very good novel, responsibly."
Ashley agrees, and says children's writers know the limits to what they can say. "We won't sell books if we go too far" is the attitude. Agents and publishers won't take them, nor will schools.
Significant too, is the meaning of children's literature now. Serraillier's novel The Silver Sword - like War Horse, Carrie's War and The Machine Gunners - can be read and enjoyed by children as young as eight or nine. But Little Soldier is aimed at older children, the young teenage market, which is a relatively recent creation of the publishing industry.
However, not all books have age guidance, the equivalent of film certification for children's literature.
Some parents may worry whether their own children really are able to deal with the detail of wartime violence, or whether it will give them nightmares.
In primary school, pupils study World War II and the Holocaust. They read Anne Frank's diary, which many pupils find very upsetting.
And it's likely that parents in 1956 worried about Serraillier's novel, questioning whether the plight of child refugees in post-war Europe was a fit subject for young readers.
Once Upon A Wartime is on at the Imperial War Museum from 11 February 2011