Lauren Child: These childish things

Lauren Child looks ruefully at the dirty pink blanket of petals. "It was sunny for weeks before the cherry blossom came out and now it's all blown off," she says, shivering as she discards her grey jacket. We are standing in what feels like a secret garden, tucked away in Mayfair, while The IoS photographer grabs a few quick shots of the author-cum-illustrator before she turns blue.

If this were a scene in one of her wildly popular Charlie and Lola books, then Lola would be quizzing her older brother about why nothing good lasts for ever, like pretty blossom, or snow, or birthdays. Charlie, being Charlie, would probably give a quick life lesson on how too much of a good thing gets boring, while throwing in a bit of basic biology about the changing seasons for good measure.

But in this instance, for once, he'd be wrong because the pair will spend the whole year celebrating their birthday. Their extremely exciting 10th birthday, that is, because a decade has passed since Child, 44, first created the characters in the now seminal I Will Not Ever Never Eat a Tomato, although their actual ages will remain forever set in stone at seven and four.

We should be toasting them with pink milk in Charlie and Lola cups, and eating birthday cake off Charlie and Lola paper plates, while playing our Charlie and Lola Favourite and Best Music Record – just some of the 500-plus items dedicated to the duo on Amazon. Instead, we retire to the Connaught Hotel for tea and biscuits where Child plays down her phenomenal success. "It is quite surprising. But I had to do something. Plus there were years of failure before, so it all evens out," she says, her soft voice picking her words carefully.

Child – her real name, although she was christened Helen, not Lauren – is being modest. In the 11 short years since her first book was published, Clarice Bean, That's Me, she has become the eighth most frequently borrowed author from UK libraries; been made an MBE for her services to literature; and been a Unesco Artist for Peace for the past two years. Even America has fallen for her charms: New York's famous FAO Schwarz toy store has an entire wall devoted to Charlie and Lola merchandise. She also has a string of fantastical stories such as Who's Afraid of the Big Bad Book?, other characters such as Hubert Horatio, and she is working on a new six-part series for teenagers featuring Ruby Redfort, the undercover schoolgirl agent who is Clarice Bean's favourite literary heroine.

Not that success hasn't had its price. Letting a production company spin off a 78-part animated series from her three original Charlie and Lola books may have seen sales rocket to more than three million worldwide, but Lola isn't Lola any more, to paraphrase from one of the episodes. "I think she's probably just that little bit more manipulative than I see her. In my books she's just that child who asks 'why?' but it's hard to keep that innocence over 80 episodes," Child explains. And Charlie, know-it-all Charlie, suffers even more. "We find it really hard not to have him be too goody-goody," Child admits, conceding that Charlie is the older brother that she and her older sister "were desperate" to have had.

To crack the States, she had to bow to its rules, dropping such Lolaisms as "I will not ever never" for what Americans deem the grammatically superior "I will never not" although, as Child points out: "The whole point is that she doesn't speak properly." The Americans also had a problem with her Clarice Bean series, refusing to publish My Uncle is a Hunkle under that title because "they said hunkle doesn't mean anything," Child adds. "I said, 'Well it doesn't mean anything in England either'."

The animation, too, is a cruder version of Child's own work, a delicious collage of delicate line drawings, bold prints and photographs. There are still plenty of Child touches, however. The material for Lola's pyjamas, for instance, comes from a dress Child's mother made for her when she was a baby. "I just photocopied it; it seemed right." The brown wallpaper, which like most of the furnishings in Charlie and Lola's flat has a retro appeal that resonates well with the parents doing the reading, was created from a swatch of fabric left over from the brief time Child attempted to make a living selling lampshades. ("We called ourselves Chandeliers for the People, taken from Marie Antoinette's 'Let them eat cake,'" Child says.)

The retro choices are deliberate because Child set Charlie and Lola in her own idealised 1970s childhood. Unlike Child, however, who grew up in Wiltshire, where her father headed the art department at Marlborough College, the brother-and-sister pairing notionally live in Copenhagen. Which explains the clean living and funky decor. Child's inspiration for Lola came from a young Danish girl she saw once on a train in Denmark. "She had these eyes that went up like a pixie and was wearing a little dress over some trousers. She looked incredibly sweet." The nameless girl in question, who has no clue that she spawned a global children's franchise, haunts Child. "I think about her a lot. In some ways it's really sad because I'd love to see her again but there is no way of ever, ever chasing that girl."

Child, who peppers her own speech with plenty of the adverbs beloved by Lola, admits to having something of a Scandinavian obsession: she has a Danish ex-boyfriend – who is still a partner in her business, Milk Monitor – dreams of a second home in Sweden, and cites Habitat as a key early influence. Lola even has a Danish imaginary friend, Soren Lorenson, although the childless Child puts paid to any suggestion that there is anything Freudian about the homonym Soren Lauren's son (even if her ex-partner is called Soren). "That's rubbish," she says, explaining that Soren Lorenson, who will star in a fourth original Charlie and Lola book this autumn, Slightly Invisible, was "a real person" in as much as he was her own friend Sophie's pretend friend when she was small.

Swedish aesthetic aside, I doubt that Child is dressed in H&M; her black silk T-shirt with splashes of floral colour is too well cut, and her handbag is definitely Orla Kiely.

For now, though, Child lives alone in a 1930s house in Belsize Park, north London. Her lack of children is a subject of constant speculation, given her gift at writing for them; all she'll tell me is that "yes", she would still like to have some. She might not have her own offspring to turn to for inspiration, but she can recall her own childhood well. She likes to write about "very simple things, which can be a big deal when you're small" such as not wanting to eat peas, or dreading bedtime. "It's all about having to do things for the first time." Plus she has a ready supply of childish anecdotes from her many fans. "They tell you funny things about their family set up, like 'My dad had an argument with my mum last night and he slept on the sofa'. Often they write over and over. I got this one postcard from this girl who said, 'I'm sorry I haven't been in touch; I've been in Italy.'" She also rates eavesdropping. "When people talk on their phones it's as if they have forgotten anyone is listening. People lose all sense of privacy – it's really strange."

Then there's always the television: "I find that very inspiring if I'm stuck." Controversially, she reckons she owes a lot of her success to the box. "When I was a child I watched a lot of telly. I know it's frowned on but in fact it's really paid off. Obviously I'm a big fan of reading and looking at books, but I don't think all television is bad because I think what I got from it was an understanding of stories and characters and what draws you in. It led me to books as well because I wasn't a natural reader like my sister, but after I saw Little House on the Prairie or Anne of Green Gables I read every single one of those books." Her new character, Ruby Redfort, "comes from watching Seventies cop shows and those early Jodie Foster films she did for Disney as a child."

Despite requesting that we meet in a hotel, Child says she "loves looking at other people's houses", whether they are National Trust-type affairs, or visiting friends. It stems from her fascination with home furnishings; ultimately she'd like to design homewares, her failed lampshade venture notwithstanding, and she recently designed fabric for Liberty, her favourite London shop. Child already has form dabbling in different fields: before settling into her illustrator groove she painted spots for Damien Hirst. "It was so hard to do creative things and support yourself. I really needed a job." Her task, along with other dot deputies, was to measure, mathematically, where each spot was to go, mix up "maybe 1,000 colours... we were never allowed to use the same colour twice on the same painting" and get dabbing. And no, she can't tell today which Hirsts are hers.

If nothing else, she's made good use of all that experience with colour: her books are flooded with rainbow hues. And I'm sure that if Lola ever does get to grow up, then a bright future as an artist would beckon. She's certainly extremely fond of drawing.

Curriculum vitae

1965 Born in Cold Ash, Berkshire. Brought up in Marlborough, Wiltshire

1990 Graduates from London's City and Guilds Art School, where she did a decorative arts course

1998 Works at Big Fish design for five years

1999 Publishes Clarice Bean, That's Me, after four years of rejections

2000 Awarded the Kate Greenaway Medal for Charlie and Lola's I Will Not Ever Never Eat a Tomato

2005 BBC launches a 78-part series of Charlie and Lola, which has won four Baftas.

2008 Becomes an Artist for Peace for Unesco and reissues That Pesky Rat to raise money for its education programme

2010 Is made an MBE for services to literature.