Medication, if needed, is frequently anti-depressant medication. There are a number of these medications that have been approved for use in children, but their use should be closely monitored and parents should be made aware of the side effects to watch for.

Sources:

Separation Anxiety and Separation Anxiety Disorder, 2006, Jaffe-Gill et al.,  Helpguide.org

Separation Anxiety, 2005, Reviewed by Michael J. Harkness, MD, KidsHealth.org

Separation Anxiety in Young Children, 2004, Carol E. Watkins, MD, Northern County Psychiatric Associates