This was a library book I read in elementary school in the early 1970’s, so I am guessing the book was likely published sometime in the 60’s.  To the best of my memory, it involved a brother and sister in South America who somehow offended the sun (it could have been the moon, but I am pretty sure it was the sun) and the sun came right out of the sky and rolled after them, chasing them up and down hills.  I remember the sun being quite scary and it having a mouth that was illustrated very similar to a zipper on clothing.  Any help you could provide would be much appreciated.