Libby Rees is an exceptionally composed 10-year-old with a highly developed emotional vocabulary. “If you write down how you’re feeling then it goes through the pen into the paper,” she advises. “If you burn it you can actually see the paper going up in smoke. It’s almost as if all your problems go with it, just fading away as the paper curls. And you’ll feel a lot happier.”

Blimey. As I said, Libby is 10, and when she came up with this extremely grown-up cognitive therapy technique she was 9. That is when she wrote her book, Help, Hope and Happiness, a manual for children like herself who have faced difficulties. It is a short book of 2,200 words, but no less profound for that, and it will be published next month in response to Libby’s observation that there is a gap in the market waiting to be plugged.

“There are lots of stories of children who are unhappy and I’m surprised there aren’t more self-help books for kids. Kids have got quite a lot to deal with,” she suggests.

We are in a London hotel with her mother, Kathryn Loughnan, squeezed into their schedule between a BBC interview and Richard and Judy. Today they fly to New York to talk to ABC. Libby says this is all very exciting, although she is so tiny and still that she doesn’t sound moved.

But then, as her mother says, Libby is a thinker, and that is why she has not only come up with the 30 homilies that form her book, but found a publisher. She wants to help other children, she says earnestly, and to that end she will donate two-thirds of the royalties to Save the Children. Naturally her mother, a special-needs assistant, is very proud: “I feel like a student to this wise person in a 10-year-old body,” she comments.

Well, faced with so many precocious thoughts on positive thinking and anger management from one so young, you would. So where have these thoughts come from, I wonder. Kathryn insists that Libby wrote “without adult interference” and that the publisher declared that not a word should be changed (though I do hope they correct the spelling of “Carpe Deum”). So, inevitably, the techniques Libby recommends came out of her own experience of family life which, three and a half years ago, was severely jolted by the breakdown of her parents’ marriage. You will not find a reference to this in Libby’s book, but this is nevertheless the substance of the marketing campaign behind it: 9-year-old gets publishing contract for her tips on how she coped with her parents’ separation.

In an era where divorce is commonplace, Libby’s contribution is surely significant. She lives in Ringwood — “a small market town on the outskirts of the New Forest,” she says helpfully — with her mother and 17-year-old brother Luke, whom she describes as “very supportive”.

I am astounded by this mature vocabulary, but Libby says she picks it up from conversations between her mum and Luke, and she reads a lot. She likes Michael Morpurgo, Dick King-Smith and Charles Dickens, she says, though it turns out that she hasn’t actually read any Dickens yet, but has watched some of the films.

I wonder how she felt about her parents separating. “At first I was sad but now I’ve grown up because it happened when I was 6 and now I can understand they didn’t get on any more and I know it happens to lots of people. I don’t really mind any more. I sort of felt . . . no . . . in a way . . . like I said, I really don’t mind any more.”

This is how our conversation goes: for one so emotionally literate Libby is sphinx-like in her reactions. I put the question in a different way and her response has the dexterity of Charles Kennedy when asked how many of his Liberal Democrat team have advised him to step down as leader.

What makes her happy? “Playing the guitar, swimming, reading, dancing, writing. That’s about it.”

What makes her sad? “Sprouts,” she replies. That, I admit, is masterly.

But she does mention “the people from the court welfare” who visit her periodically and it emerges that, at her own request, she has not seen her father for three and a half years. “I find it a lot easier to have one home and not be going between two places,” she explains, though her father continues to seek access to his children through the courts.

Times recommends

• Live chat: Thrifty ways to update your winter wardrobe
• Is anybody out there really listening?
• Nutrition Q&A: Will eating late make me fat?