The objective of this narrative review of the literature is to describe the epidemiology, etiology, pathophysiology, diagnosis, and treatment of pediatric anxiety disorders. We aim to guide clinicians in understanding the biology of anxiety disorders and to provide general guidelines for the proper diagnoses and treatment of these conditions early in life. Anxiety disorders are prevalent, associated with a number of negative life outcomes, and currently under-recognized and under-treated. The etiology involves both genes and environmental influences modifying the neural substrate in a complex interplay. Research on pathophysiology is still in its infancy, but some brain regions, such as the amygdala and the prefrontal cortex, have been implicated in fear and anxiety. Current practice is to establish diagnosis based purely on clinical features, derived from clinical interviews with the child, parents, and teachers. Treatment is effective using medication, cognitive behavioral therapy, or a combination of both. An introduction to the neuroscience behind anxiety disorders combined with an evidence-based approach may help clinicians to understand these disorders and treat them properly in childhood.