I remember reading a story/stories in the 70's about a boy and girl who could fly using a backpack/pouch that had cords that they had to extend to their hands (this became a crucial item in the story as one of their cords got broken/cut and couldn't fly at a key point in the book).
There were some monsters that they were trying to get away from and I remember that they were following them (while in a car?). The author mentioned something about "racing the moon" and it comes back to me every time I drive a car on a moonlit night.
Sorry this is so vague but it was a very long time ago. I remember enjoying the story and would like to pass it on to my Daughter who is a voracious reader like myself. Thanks