That book, like most she has written since, took between three and six months to complete.

"I have an over-flowing waste paper basket and the words take me a really long time," said Vulliamy. "Sometimes I can spend all morning writing one sentence and all afternoon rubbing it out."

Vulliamy is best known for her books The Bear With Sticky Paws and Martha and the Bunny Brothers. A new book, "I heart bedtimes (Martha and the Bunny Brothers) is due out in the UK on March 28.

Her illustrations are bold, simple and are usually of fully-clothed, talking animals; very different from her mother's intricate and realistic drawings of children.

At 85, Hughes has cut down on her traveling, but has no intention of retiring from her writing.

"I would much rather not retire at all," said Hughes. "I love working, and a full morning's work is still very much part of my daily routine."

Shirley Hughes will appear with Clara and her two sons Ed and Tom Vulliamy in a talk called "Keeping it in the Family" at Oxford Literary Festival on March 16.