A mega-star was in town last week, playing to sold-out houses, mobbed by adoring fans. She's an unassuming 60-something, and unless you have children, chances are you've never heard of her. For literate parents, Julia Donaldson would be hard to miss. She's written over 100 children's books, poems and plays, including the decades-long best-seller The Gruffalo, with Axel Scheffler's wonderful illustrations. The story of a little mouse who invents a monster to scare off predators, and then discovers that the imaginary monster is real, was hailed as a modern classic and took her from a modest life as a freelance songwriter to literary super-stardom.In 2015, she was the UK's top-selling author. Not the top-selling children's author, mind you, the top seller overall. In 2014, 40p in every £1 spent on picture books in the UK was spent on a book by Donaldson, according to an article in The Guardian.What made The Gruffalo so successful? "That's a bit like asking the archer what it's like being shot by the arrow. I can't really say. I suppose it's a mixture of things. The language. It's a very good plot. Right from the beginning there was a real buzz about The Gruffalo. There was something in the timing of it. Perhaps now a rhyming book about a monster doesn't seem unusual, but in 1999 children's books were a bit lovey-dovey."Her days as a busker and a songwriter have stood her in good stead. With her husband Malcolm on guitar, she has a popular show in which they sing and act their way through her stories. The shows at the Linder Auditorium were sold out, packed with moms and kids who knew every word, and who queued out the door for book signing.The show is good old-fashioned fun, with clever rhymes and jaunty choruses to sing along to. It's rather like having your funnest sprightly grandparents entertaining you. Kids from the audience take the parts of farm animals. Props are simple - a bolt of blue fabric for the duck pond, a set of furry mouse ears on a head band. The highlight is the appearance of the Gruffalo himself who, despite "his terrible tusks and terrible claws", not to mention "his turned-out toes and a poisonous wart on the end of his nose" falls just on the friendly side of monsterdom. The crowd goes wild.Young children are obsessive, which for parents means reading the same book again and again. A book that can stand the test of hundreds of bedtime readings is rare."I love the fact that my books are bought and read by parents. The bedtime story is a healing, companionable experience. It's nice to feel that you're contributing to that lovely bond between parents and children," Donaldson says.She says of her craft: "What usually happens is I have the germ of an idea, or a character. The story doesn't come out fully fledged. Only when I have worked it out in my head, with a clever twist, do I start crafting the language, the chorus or recurring motif. With my song-writing background, that comes quite naturally. It's the middle bit that's difficult, coming up with a story that is original, satisfying and not too predictable."Donaldson loves fables, but she never wants to preach: "I don't think 'why can't children be kinder to each other, I'm going to write a book about it'. But neither would I write a book which is just a string of co-incidences, you know, 'and suddenly a monster appeared'. Any story worth its salt has its underlying truth."It's this truth that has made her the rock star of children's literature. We wrap up our interview so Donaldson can head off to a store visit.They have had 500 RSVPs, and who knows how many more fans will pitch up. Donaldson and the publicists both seem quite taken aback at the outpouring of South African fans.She says:"I've never felt so mobbed as I am here. Someone came up to me in the loo and asked for a photo!"..