1. Kids like chaos... but only a bit of it.

The Hogwarts school set up in the Harry Potter books is perfect. Kids love the idea of being away from the comfort of home, but are also deeply attracted to a sense of stability and find too much chaos too scary to contemplate. Being in a school situation is something they can relate to, and adding the -magic- element adds the necessary frisson of excitement that takes it just far enough out of the ordinary. The fact that the magic school is a cliche long used and abused in fantasy fiction, and lampooned succesfully by Terry Pratchett, goes straight over the heads of the bulk of HP readers, purely because the target audience is too young to recognise the antecedents.

2. Kids like adults to be larger than life... but not all the time

And there's no bigger than Hagrid! Kids like their adults in fiction to be larger than life, and slightly eccentric. By populating Hogwarts with over the top personalities with many childlike characteristics it lets kids live out fantasies of relating to adults as equals without the stress of actually having to talk to real adults. And these child-like adults, and the father figure Dumbledore in particular, have to act responsibly when it comes to all the big decisions, just like parents in real life.

3. Kids like to be independent... but have friends close by

And where would Harry be without Ron and Hermione? Harry is just sufficiently independent to be cool, and close enough to his friends to be reassuringly normal. The angst of Harry's home life with the Beasleys is nicely counterpointed with his friendships to allow kids to relate to both.

4. Kids like to be scared... but only a bit.

And JK Rowling ramps up the scares to just the right degree, putting the friends in harms way on a regular basis, only for Harry to save the day with his bravery. And kids love the idea that they too would be just like Harry in such a situation.

5. Kids like new games... and old ones

And Quidditch is such a potent mix, of hockey, football and speed racing that, combined with the flying broomsticks, allows kids to play the game themselves in their heads, going far beyond the mere words on the page.

6. Kids like new ideas... and old ones

The whole Harry Potter series is a mixture of new and old ideas. JK Rowling has taken many fantasy tropes and mixed them with original ideas. The kids, although they might not even recognize it, are already steeped in the basics of storytelling through fairy tales and fables. JK Rowling has built on the basics, and in doing so created the ultimate in children's fantasies.

As writers, all we have to do to join her is understand the kids in the same way that she does. And it helps to be Scottish.

Simple really.