I don’t have just one book to recommend. I have several series for kids aged 8-12.
The first: the Young Wizards series by Diane Duane, beginning with So You Want to Be a Wizard (for ages 10 and up). This series is about Nita and Kit, two friends who found copies of a book entitled So You Want to Be a Wizard and were brought together. They must learn to use their wizardry while battling to postpone the universe’s death.
The second: the Unwanteds series (for ages 8 and up) by Lisa McMann. These books tell the story of the land of Quill, where creativity is a crime, and those caught committing it are sentenced to death. But the sentence isn’t exactly what is seems.
The third: the Michael Vey series (for ages 12 and up) by Richard Paul Evans. A prototype imaging machine malfunctioned, and of the 59 people born in that hospital during its test period, only 17 survived. These children acquired electrical powers. A madman makes it his goal to use them to take over the world, and gets all of them except Michael Vey.
The fourth: the Blackwell Pages series (for ages 8 and up) by K. L. Armstrong and M. A. Marr. This trilogy is about the descendants of the Norse gods and their battle to prevent the world from ending. It begins with Loki’s Wolves.