There’s nothing new under the sun, but some people can take an old idea and make it as fresh as a daisy.

Cressida Cowell was brave, possibly to the point of foolhardiness, when as a first-time children’s writer and illustrator, she stepped into well-trodden Ahlberg territory.

Here reside the masters of the Jolly Postman trilogy (The Jolly Postman and Other People’s Letters, The Jolly Christmas Postman and The Jolly Pocket Postman). Janet and Allan Ahlberg have enriched the imagination of generations of children with these books, now classics.

They play hilariously irreverent word and story games with traditional nursery rhymes and tales, layering text upon text and adding entertainment value with pull-out letters and postcards. Very traditional narrative themes and characters are made to sing for new generations.

Better to leave well alone, you might think. Others have strayed along the Ahlberg margins, but to claim a full stake in the territory requires considerable audacity, skill and flair. Cressida Cowell pulls it off.

Little Bo Peep’s Library Book (Hodder Children’s Books, pound;12.99) takes us into a world inhabited by nursery rhyme characters and employs the same kind of clever contextual jokes. So there are removable books within the book - indeed, a built-in library.

Cowell borrows unashamedly from other writers, transforming their ideas into something her own through the twist of her wit and the brilliance of her illustration. Here is an artist who understands the use of colour and composition along with the best. These pages are so funny, light and fresh, sparkling with colour - pinks and purples, oranges, blues and greens - enlivened by quirky line drawing, simple and generous, that will attract children.

As the Jolly Postman series developed it became ever more complex, the layers of pictorial and literary devices breathtakingly supple and subtle. Cowell creates something bolder and simpler.

Little Bo Peep has lost her sheep (no surprises there) and is referred to the Mother Goose Library for books on how to find them. A slightly baffled Mother Goose, the librarian, sends her to the cookery section. Here she meets that familiar backwoodsman Monsieur Loup, licking his chops and reading Basic Little Girl Cookery.

He refers her to the crime section, where she finds the Queen of Hearts reading Who Stole the Tarts? by Mrs A. Summers-Day. Eventually the natural history section yields How to Find Sheep by A. Shepherd. The wolf trails her around the stacks, plagued by thwarted intent.

If ever there were a book to encourage small children to use the library, this is it. It comes with a date-stamped library ticket and a cataloguing bar code, as do the simple books inside. These little books, complete with publisher and price (for example Baa-Baa Books, pound;4.99) designed to withstand the developing motor skills of small children’s hands, pull out from the library shelves among other delicious titles such as My Sad Childhood by Tom, Tom, the Piper’s Son.

Monsieur Loup’s Basic Little Girl Cookery is a delightfully macabre recipe book, laced with boy-appeal and Roald Dahlish flavours. For example in “Mary Mary a la Mer” cooks are reminded to “remove armbands andor rubber ring as too tough”. Indeed, the references and jokes will keep older readers grinning from ear to ear through several repetitions.