Here are two more books you might want to try if your child tends to worry a lot, which are on my pile of books waiting to be read:
Freeing Your Child from Anxiety: Powerful, Practical Solutions to Overcome Your Child's Fears, Worries, and Phobias, by Tamar E. Chansky, Ph.D.
What to Do When You Worry Too Much: A Kid's Guide to Overcoming Anxiety (What to Do Guides for Kids), by Dawn Huebner, Ph.D. (for younger children, between the ages of 6 and 9)
Here are the other related posts, in case you missed them:
I hope you have a very relaxing weekend!