From the swishy-swashy grass to the splash splosh of the river and squelch squerch of thick, oozy mud, We’re Going On A Bear Hunt has delighted a generation of youngsters since Michael Rosen’s beloved book was first published in 1989.

Now the hit bedtime story has been adapted by the makers of The Snowman into a charming, 30-minute animated film, which airs on Channel 4 on Saturday night.

Featuring the voices of Olivia Coleman, Pam Ferris and Mark Williams, the simple story revolves around siblings Stan, Katie, Rosie, Max and the baby, plus Rufus the dog, who decide to go on an adventure in search of bears.

Rosen, a former children’s laureate and poet, described the animation by Lupus Films, which comprises 100,000 beautiful drawings, as “utterly amazing”.

Having sold more than eight million copies worldwide and been translated into 18 languages, We’re Going On A Bear Hunt was awarded the Nestlé Smarties Book Prize the same year it was published and is still a bestseller more than 25 years later.

But if you ask Rosen why the book has been so successful, he will modestly defer to illustrator Helen Oxenbury, with whom he collaborated on the original book.

“In one respect I’m the least qualified person to answer this,” jests Rosen, who grew up in a Jewish family and spent much of his childhood living in Pinner.

“I’m utterly ashamed of this, but when I first saw Helen’s drawings, I had no idea what the pictures were to do with the story.

“It was only when the book came out that I realised that in the greatest of children’s books, what actually happens is you start off with a situation where a parent is sitting with a child on his or her lap, they are sharing the book and the parent is saying the words, but the child is looking at the pictures.

“The words don’t say anything about the drama that Helen has created. The child will say things like ‘teddy’, ‘dog’, or ‘grass’, and they begin to anticipate it, so they are the interpreters of the story and it’s a tremendous way of giving power to the child.”

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We’re Going On A Bear Hunt has been transformed into a charming, 30-minute animated film, which airs on Channel 4 on Saturday night

That said, the “pounding rhythm and repetition” of the words are signature Rosen, inspired by an American folk song he once heard and decided to adapt for performing at schools.

Rosen, who turned 70 earlier this year, explains: “The thing that really caught me about We’re Going On A Bear Hunt is the repetition and how if you do it with young children they learn it as they go along.

“So even in a first performance you just start with ‘We’re going on a bear hunt, we’re going to catch a big one’; however you do it, by about the third verse they know it. That’s very infectious. Anyone who performs wants things to be infectious, particularly with children.”

It was during one of these lively performances that David Lloyd, head of Walker Books, approached Rosen and asked him to write the children’s book, teaming him up with Oxenbury for the illustrations.

The talented father-of-five was again approached for his script-writing skills in this latest film adaptation, in which he voices the bear and for which he has tweaked the storyline to show a relationship between the children’s grandfather, who has recently passed away, and the animal.

On this issue, co-director Joanna Harrison said at the film’s recent launch event: “One of the lines is ‘It’s OK to be sad’, and my godmother once said to me you can’t have happiness without sadness, the two go hand in hand. If you want happiness, you have to accept you are going to get sadness.”

Call The Midwife actress Pam Ferris, who voices the character of Grandma, adds: “It’s stating the obvious, but [as the book says] you can’t go over it, you can’t go under it, and in life there are just some things you have to go through – and grief is one of them, there’s no way round it.”

Personal tragedy is something Rosen himself has experienced, following the death of his 18-year-old son Eddie, in 1999, from meningitis.

We're Going On A Bear Hunt

Michael Rosen, author of We’re Going On A Bear Hunt, lends his vocal talents as the bear for the animated version

His unexpected loss inspired him to write Carrying The Elephant: A Memoir of Love and Loss, as well as Michael Rosen’s Sad Book, both of which deal with bereavement.

Yet for all its poignancy, We’re Going On A Bear Hunt certainly ends on a happier note.

“The story shows there is this danger – and you survive this danger,” he concludes. “So what you learn through fiction is that you do survive, there is a utopian, optimistic feeling at the heart of it, that you can survive, you can get through this stuff.

“And that’s what you get from it each time you read it or hear it. That’s the real power of the story.”

We’re Going On A Bear Hunt airs on Channel 4 on Saturday (Christmas Eve) at 7.30pm.