In a magical world the rules of physics do not apply. Things float, people transform and travel through time and space. They appear and disappear. Often what matters is a hidden talent and, perhaps, a special object or substance. The usual rules do not apply.
But the funny thing about children's books set in magical worlds is that they are all about rules. Rules govern how magic can be used. Knowledge of the rules, especially the words to use, determine everything.
In Harry Potter, for example, the rules governing horcruxes largely determine the action of the final parts of the series.
Of course, maybe the most overreaching rule in the whole series is that magical folk remain secret. I have some sympathy for Voldemort (gasp!) and the Deatheaters. What's the good of all that magical power if you have to keep it secret? You can't very well be the ruler of the world if nobody knows who you are and what you can do. Voldemort is about breaking the rules. He doesn't want the rules of physics and biology or magic to apply to him.
The thing about rules and why this is so much fun for kids (and adults) is that this is how games work. Harry Potter is a game (a deadly one for the books' characters) where the enemy's flags (the horcruxes) are captured and destroyed. In real life, all the drama about the horcruxes is kind of ridiculous. So much business. What does it matter? But that's how games work. And it's the quality of the rules that make games (and books with magic) interesting.
The next time you read a book with magic in it, think about the underlying rules. They are one key to how successful the book is.
I'll be reviewing some magical books in upcoming posts.