20% of children have an anxiety disorder. It may be generalized anxiety where kids worry and have enough fears to affect their function, or separation anxiety where they have such fear about being apart from a parent they can't sleep out or have trouble going to school or being apart at all. Another is social phobia where there is such self consciousness about being with other people that the child becomes isolated from making new friends.
When these disorders are left alone many children go on to develop depression or even substance abuse as a result. It is important to seek treatment for your child and the great news is that treatment really works and will be bring relief to the entire family.