I was interested in this article, Three Elements of a Killer Title. I've struggled to find a title for my first book, currently appearing as Peregrin Zefyr and the Timehiker - not my favourite choice, but the nearest I could get to something that did the trick, IMHO ... and which had not already been bagged by somebody else.
I was not short of ideas, and they must have been good ones. I googled each one as I thought of it, and most of them are already out there attached to recently published books for children.
According to the writer of the post, the title needs to represent the story, add intrigue and sound good. I'd have to add, you also need to be the first person to think of it.