One Direction is writing, and this time, it's not a song but a story book for kids.

Harry, Niall, Louis, and Liam are four of the 25 artists who penned the book called "The Curious Tale of Fi-Rex" for the "Children in Need" charity, reports Mirror.

"The Curious Tale of Fi-Rex" is the story of a little half-human half-dinosaur girl. Each celebrity gets one page to write her story.

Moreover, there's a twist in how the authors continue their stories.

The celebrities cannot browse through other stories. They are only allowed to know the main character and the last sentence of the previous page to get a clue of how to carry on.

"I was told who the main character was and I was shown the last sentence of Wayne and Coleen Rooney's part of the story, and I had to carry it on in my style," actress Denise van Outen told Mirror.

In Denise's page, Fi-Rex remembers the memory of home and is excited to get back.

One Direction is also making an appearance in the book - not as the popular boys they are, but as frogs - known as the frog group Pond Direction.

English pop group Take That is also up on the list. Gary Barlow, Howard Donald and Mark Owen also contributed in writing Fi's story.

Other celebrities include married couple Jamie and Jools Oliver, "Britain's Got Talent" judge Amanda Holden, recording artist Ronan Keating, TV presenter Bear Grylls, model Penny Lancaster.

Wed couple Coleen and Wayne Rooney, tennis player Andy Murray, comedian Keith Lemon, diver Tom Daley, model Kate Moss, model Annabelle Neilson, TV host Nick Grimshaw, and singer Kylie Minogue also wrote their stories.

Speaking of boy bands, Paul McCartney, a member of the legendary band The Beatles, is also on the list.

He even brought to life the frogs who were featured in his song "We All Stand Together," which is sometimes called the Frog Song.

The artist bringing the little girl to life is Julia Patton.

The original signed pages of the book are up for auction. All proceeds come to BBC's "Children in Need" charity.

The charity provides grants to UK projects which focus on helping disadvantaged children and young people. They aim to ensure that every child in the UK experiences a safe and happy childhood which will allow them to explore their potentials.

"Children in Need" is going to hold their annual "Need Appeal Night" this November. The event features celebrities singing, dancing and doing other things that will help raise money such as the "Fi-Rex" book project.