There is a primary school across the road from Cressida Cowell’s west London home, so the author of the How to Train Your Dragon series writes with a backdrop of shouts and yells from the playground. The little garden shed where she dreams up and illustrates the stories of Hiccup Horrendous Haddock III and his dragon Toothless is stuffed with drawings and maps, pencils and paints, and piles and piles of books.

“I have been into that school but not recently, so maybe I’m incognito to this generation,” says Cowell, who has lived in the area for decades. She does sometimes get recognised when she’s out and about. After all, she’s sold over 11m books around the world, in 38 languages, with her How to Train Your Dragon series – her story of a Viking boy who becomes “a Hero the Hard Way” – now adapted into a billion-dollar DreamWorks film series, as well as a TV series on Netflix and CBBC. Also, she says, “children come up to you in a way adults wouldn’t. It’s one of the great things about the job.”

She is about to get a lot more recognisable, as the eleventh writer to take on the two-year role of Waterstones’ children’s laureate, following in the footsteps of Quentin Blake, Malorie Blackman and Jacqueline Wilson. When she was announced as the latest incumbent on Tuesday, she unveiled her Laureate Charter, a “giant to-do list” which asserts every child’s right to “own their own book”, to “be read aloud to” and to “see themselves reflected in a book”. “I’ve got two years,” she says. “I’m a practical person. If you’ve got a giant problem you need a giant, practical to-do list.”

And here is my @Waterstones Children’s Laureate Reading Charter (or giant ‘TO DO’ list...) I love a quest. pic.twitter.com/OOIoOdxGKA — Cressida Cowell (@CressidaCowell) July 9, 2019

But she admits it’s not going to be easy. “There’s not a quick fix: ‘We’ll make this little tweak to the curriculum and everything will work out.’ It’s a complicated problem, and the stakes are really high. Reading is a medium we cannot lose. I love films and telly [but] they get magically beamed into kids’ heads, whereas with books it’s much more of an effort. Books can easily represent something that makes kids feel stupid, and how can you love something that makes you feel stupid?” Her ultimate aim is to get children “as excited about reading and books as they are about films and telly”.

“Because – I’ll just hit you with it,” she says, leaning forward in her armchair in excitement, “because books are a kind of transformative magic that offer magical things that films aren’t as good at creating in children: empathy, creativity and intelligence. With a film, things happen out there, in a book it’s happening inside your head, so that’s empathy. Creativity – a book is partly what I say and partly what a reader imagines, whereas films are very bossy, they tell you how things would look and how they would sound. Intelligence is words. Those are the three magical powers, that’s why books have to survive – because, my goodness, we need empathetic intelligent creative people today.”

Cowell says she “always had stories I wanted to tell”. She grew up in London, daughter of the environmentalist and hereditary peer Michael Blakenham, and the family spent holidays on a small, uninhabited island off the west coast of Scotland. There was no television, “so I was writing a lot, reading a lot, we were making up our own entertainment,” she says. “We’d be dropped off by a local boat and picked up again two weeks later … we’d spend the whole summer on the island once my dad had a house built. It was the first place the Vikings came to in Britain and the last place they left, so real Vikings lived on the island. We’d play and look for dragons in the caves, because Vikings believed dragons really existed.”

I wasn’t an instant success. I talk about that in schools, because children are not necessarily getting that message

She read English at university, worked in publishing for a time and then went to art school because “I quickly realised I wanted to be on the creative side”. She wrote her first book while she was there – Little Bo Peep’s Library Book, a charmingly funny picture book with pull-outs in which Little Bo Peep has lost her sheep, and goes to the library for help with finding them. It was published in 1998, “when my daughter was born; it was a race as to what would come first, the book or the baby,” she says. “I think picture books are fascinating, they’re like writing haikus for aliens.” She wrote a handful more picture books, including the first Hiccup story, The Viking Who Was Seasick, drawing on her childhood games on the Scottish island. She still has the handwritten original, pieced together from torn-up pieces of paper.

“For about five years, I was writing these picture books which people weren’t jumping up and down about. I wasn’t an instant success. I go in and talk about that a lot in schools, because children are not necessarily always getting that message,” Cowell says. “That’s the reason Hiccup’s sword is known as Endeavour.”

She moved into chapter books for intermediate readers because she had “more stories to tell” about Hiccup’s world, and picture books weren’t quite big enough. It was an easy transition. “My problem generally is I have too much to say and not enough time to say it, so actually I relished the space.” She knew from the start where the 12-book series was going to end. The first novel opens with a note from Hiccup: “There were dragons when I was a boy … You will have to take my word for it, for the dragons are disappearing so fast they may soon become extinct.”

‘The films help pull in new readers’ … How to Train Your Dragon: The Hidden World Photograph: Allstar/Dreamworks Animation

“I had written a lot of the last book really early on,” she says. “Hiccup’s story is that of a hero going on a journey without realising it, so I had factored in that it would be a long series and not a direct line. I had this massive thing on the wall in my shed with all the plot lines, it was very complicated.”

Part of the reason she wanted to write a long series was because “you start a quite good reader, and by the end you’re a really good reader”. “All the spelling tests in the world can’t teach you what you learn from reading the whole of How to Train Your Dragon or Harry Potter or Artemis Fowl. Without having to learn word lists, you just absorb all this.”

Children love the magic in the books, she believes, because “they do get bossed around all the time and magic makes you powerful”. And they also respond to the parents in her stories needing to learn from the children, as well as the other way round. “It could have been How To Train Your Mum. There’s a lot of thinking about what we need to learn from children and what the experience of parenting teaches you, because children are really interested in the essential things in life, and often adults get lost along the way.”

In her books, she says, “the story is told in a get-you-through-the-story kind of way. These are clever mass-market books … So they are visual, because kids are more visual nowadays, but they’re not dumbed down, because kids are smart.” What becomes clear is that Cowell writes not only for the joy of the stories, but because she is so passionate about getting children reading; she’s already an ambassador for the National Literacy Trust and a trustee for World Book Day, and she fizzes with advice and energy. “Listen to your kid read in the morning before breakfast rather than making it a big fight,” she advises. And, “it doesn’t matter if they’re reading picture books beyond the age they ‘should’ be. That’s often the way in.”

“There’s so much competition for children’s time and attention,” Cowell says. “Part of the whole way I write has always been to get children reading.” But writing for a young audience hasn’t held her back. “I don’t feel inhibited. What am I missing out on, in writing books for children? I’m writing about heroism, about love, about what kind of leader we deserve.”

Film rights were acquired for the series in 2004, when she had just published the second book, but she “never thought they were going to make it, because they normally don’t”. When the first film was released in 2010, it brought an avalanche of new readers. “One of the big advantages of having your books turned into films is that you do reach children who don’t necessarily get that books are great, and you pull them in. The books and the films have really helped create new readers, so that’s what I hope will happen [with the laureateship], that I’ll be able to reach kids who don’t realise it’s the How to Train Your Dragon lady.”

The two areas she will be focusing on as laureate are libraries and creativity. She will be campaigning for libraries to be statutory in every school, and for public libraries to be properly funded, as well as expanding her Freewriting Friday campaign, which she launched with the National Literacy Trust last year. This asks schools to give each child a blank book, and for 15 minutes every Friday they can write what they want and teachers can’t mark it.

She shows me her own notebook from when she was eight; she’s spelled her name Crissida, but there are pages and pages of writing and drawings of elves. “My lovely teacher allowed me to just do this and that’s where I discovered the joys of writing, having some space where my spelling and my handwriting didn’t matter,” she says. “What I’m doing here may just feel like mucking about, but it ended up being something concrete that has turned into books being published, films being made.”

As for libraries, they have for Cowell always been key. “If your parents can’t afford books and your primary school doesn’t have a library because they’ve been shutting over the last 10 years and you don’t go to the public library, how do you become a reader? How is that supposed to happen? Nobody has been able to answer that question effectively for me. At the very least primary schools have to have libraries.”

But most of all, she wants her laureateship “to be about joy”. “I’m going to make my laureateship all about magic, about the magic of reading, of writing. As soon as it becomes something you’ve got to finish, it’s a task,” she says. “It’s got to be joyful.”