Lauren Child's new girl detective So Ruby (now that she has come to life in what will be a series of her own) is not just a girl-detective, but Clarice Bean's idea of a girl-detective. There is a brilliantly spoofy joy to her: her life is like that of Nancy Drew, the Brady Bunch and Samantha from Bewitched combined. If Clarice is Child's favourite character to write about, then Ruby, she says, is the person she would like to be. Far beyond being sweet and pretty, Child's books are shot through with anxiety and invention. They can be wise, funny, and quite perverse. Indeed, Child's two collaborations with the photographer Polly Borland slip a good deal of strangeness in secretly. Their painstaking The Princess and the Pea is like an art joke about perspective: two-dimensional paper dolls positioned and photographed in three-dimensional sets. Their Goldilocks and the Three Bears, for which a ringleted cloth doll - complete with unravelling tights - was specially made, is reminiscent of the fetishistic forays of the Surrealist Hans Bellmer. It helps to know that Child's father, Robin, was the inspirational Head of Art at Marlborough School. Child remarks on how many of his students went on to do art-related jobs, and Cowell recalls an exercise he set when she and Child were there. It was to look at their subject without looking at what they were drawing - a rigorous act of observation that is not so different, after all, from the way Child writes and draws now. In Clarice Bean, Don't Look Now, Clarice's best friend Betty Moody moves away. Betty is a figure based on Child's childhood friend, Gina. Child, who grew up as the middle sister of three, describes that pecking order as "rubbish." The arrival of Gina made all the difference. "It's really hard to put a value on meeting that person," she suggests, "because I think it can completely change your life, and the way that you understand relationships." When Gina's father got a job in Worcester, the girls wrote to each other (Child still has the stacks of letters), but eventually, her friend made other friends and she had to let go. "I always see the last book as a sort of tragedy," she says of Don't Look Now, "because it's about loss - and whether you break up with somebody or somebody dies or you've lost your friend when you're 11, they're all the same. I've never forgotten my friend leaving, because it was my first experience of knowing that something that feels so good can just go. This sort of subtext, she says, is what the children who write to her pick up on must frequently, and most immediately. "Children always seem to get that," she explains, "whereas if you read your book reviewed they say: "a jolly caper with Clarice Bean," and you think: No, it isn't... Generally, I think we skim over these things," she says, "because we see them as being for children." Ruby Redfort: Look into My Eyes is published by HarperCollins Lauren Child will be appearing at the Hay Festival on June 2 at 9am.