A couple of years ago, I was given the chance to write children’s fiction for a living. It was a welcome and unexpected change of tack that has since given me pause for thought when filling in a form that stipulated an occupation.

Novelist? Sounds pompous.

Author? A grand claim before the book is out.

Writer? Nebulous, but I’d better put down something.

Not long after the deal was done, a proper, acclaimed writer reminded me of something very important about this job that had once been passed on to him by another author: we make things up for a living.

That description remains my preferred one. I now make things up for a living. Which – ha ha – is in complete contrast to my job as a journalist.

But who was I making things up for? In retrospect it seems obvious that I was writing for younger readers. Darkmouth is a fantasy adventure set in a modern Irish town. It's about the 12-year-old only child of the last Legend Hunter charged with keeping monsters from a parallel world from invading. Except he's not very good at it.

Okay, so it has a young hero, and the description alone makes it clear I wasn’t sailing towards Booker territory, but the thing is, I didn’t simply write it for a specific demographic. I wasn’t entirely sure what age group it would properly appeal to (if any).

Instead, I wrote it for my son as something he might enjoy as he headed towards double figures. And I wrote for myself.

Unconventional hero

I wanted it to be fantastical, to feature a big universe that could be explored, to have an unconventional hero at its centre and jokes when possible. I wanted, in essence, to write something fun.

As it happens, the preteen readership is very open to this kind of thing. As we get older, we tend to hive everything off into narrower and narrower genres: sci-fi, fantasy, humour, literary fiction, popular fiction. To a young reader, the borders are not so narrow. You can’t quite chuck everything into the pot, but you can certainly mix up the ingredients in fantastic ways. There’s an openness about young readers that many adults shed, and it’s why books for that age are such a joy – and why adults shouldn’t be afraid to pick up so many of the writers we presume are just for kids.

You see that in so much of the entertainment aimed at what we might call primary-school age, and that in the US is known as Middle Grade. The quality of books, television and cinema for that young audience is extraordinary, and it means that they are au fait with rich storytelling and the wildest use of the imagination.

My short experience of judging and, on occasion, teaching that age group has taught me how much crazy imagination is bubbling away in the young mind, ready to leap on to the page without a moment’s hesitation. The stories written by kids of that age can be a riot, a raw block of imagination that has yet to be hewn into a more conventional shape. They can be funny, scary, surreal, refreshing and really, really good.

So, in order to appeal to them (and to me), how do I make things up?

The obvious answer is: as I go along. Not strictly true, perhaps, but it has been a steep learning curve that I would never have ascended without the help of a very good editor. But the openness of the readership means, for me at least, the opportunity to create a universe and wander around in it without feeling too limited in where it can bring me.

So much of the plot is drawn from “what ifs”. Sometimes from a list of them. And from those answers spring other questions and ideas and “what ifs”. And each has repercussions for the next book in the series (four are planned). If I was in business, this process would be called brainstorming. But I’m not, so please forget I used that word.

Of course, the characters have to appeal, the plot has to be tight, and it has to make sense within its own rules. But an editor can fix all that. (This is a joke. Though not for my poor editor.)

Still, I have been interested in how often I now meet people who say to me that it must be particularly tough writing for young people. Only adults say that, mind. I’ve yet to meet a primary-school pupil who has whispered ominously about how the 10-year-olds are going to eat me alive out there.

But I know what people mean. It’s not just that, despite our own experience of being young, we find them an exotic species. It’s that they are honest in a way that is refreshing. If they don’t like a book, they’ll put it down and not think twice about feeling bad about it.

But there is more to it than that. Young people are a sophisticated and intelligent audience, yet welcome even the strangest ideas without prejudice. That’s a pretty amazing readership to be allowed make stuff up for.

TIPS FOR ASPIRING WRITERS: SAY FAREWELL TO THE INTERNET

Finished your book? No you haven’t. Here are six things I’ve learned so far:

When you finish the book, you are not finished. Oh no. And not the next time you finish the book either. Or the time after that. Maybe it’ll be finished the time after that. But probably not.

When you send a finished draft of the book, a big klaxon does not go off in the publisher’s office. Someone does not shout, “Everyone, stop what you’re doing! The book’s here!” I genuinely thought this would happen when I sent my first completed draft to my editor. Secretly, I still convince myself it does.

The three stages of the editorial process were: structural edit (“I don’t understand the plot”); line edit (“I don’t understand this line”); copy edit (“I don’t understand how you could misspell your own name”).

A good illustrator not only gives extra life to your words, but changes things in all the right places. The illustrator of Darkmouth, James de la Rue, so precisely understood the visuals in my head that it freaked me out a bit.

I love working on my own, but it’s not good for my social skills. I only know how to type “hello” at this stage.

The most practical but vital piece of advice given to me by another novelist who suggested I immediately buy computer software that turns off the internet and won’t let me turn it back on no matter how much I fiddle, plead, or argue with it. I did that. I really need to use it more often.