I'm in my mid 30s now, but I used to wet the bed when I was 6 or 7. My mom read this to me, and that night I didn't. I had been to doctors, done tests, and after years of no results, this book did it.
It'll work, but I'll tell you that my realization at that early age was that it's not the book, it's my brain. Talk with your kid the morning after the first night they don't wry the bed and let them know they did a great job and it was their brain that did it, not the book. Let them know that if they want to decide to not wet the bed anymore, that's their choice. Let them read the book yof they want to, but that conversation will make an impact on them for years to come. I promise.