Kids have little worries and big worries. Sometimes these worries, like monsters under the bed, seem ridiculous to adults but are very real for children.
When kids get too caught up in their anxiety, they miss out on activities and can be miserable. If your child has a lot of worries, check out Dr. Larry Cohen's book, The Opposite of Worry: The Playful Parenting Approach to Childhood Anxieties and Fears. It's filled with stories and practical advice for guiding your children through their worry jungle and out to the field of safety where they can have fun.
In her Amazon review of the book, one Mom explained how she tried out the Stop/Go method. "Basically a game, you and your child are engaged in a 'stopping and going' activity---with your child being the one 'in charge'. I tried it out the next morning when brushing my seven year old daughter's hair...and I am still in shock with the results! As long as she has had hair, brushing has been an absolute nightmare, each and every morning. I always knew it was rooted in anxiety, but wondered if there were some other issues too because her reactions/screams/crying were so intense. Anyway, tried Stop/Go the other morning (which literally took 15 seconds) and she was laughing and begging me to keep brushing!!!!"