The Child Mind Institute is a great place to begin learning about anxiety disorders in kids. They organize information based on each disorder (e.g., separation anxiety, social anxiety, etc.) and they have a separate section about anxiety at school and school refusal. Information comes from leading researchers and clinicians.
American Academy of Child & Adolescent Psychiatry
The Anxiety Disorders Resource Center provides a wealth of information of pediatric anxiety. The "facts for families" section provides user-friendly information and videos with experts. You can also see the current medical guidelines on treating anxiety disorders, anxiety rating scales for kids, and apps designed to teach relaxation skills.
Society of Clinical Child & Adolescent Psychology
The Society provides a list of evidenced-based psychotherapies for youths with anxiety disorders. Therapies are divided based on children's age are organized by their level of empirical support.
Separation Anxiety Disorder
Dr. Steven Pliszka, from the UT Health Science Center, role-plays an interview with Maria, a girl with separation anxiety disorder. Although Maria reports several features of separation anxiety, Dr. Pliszka explores possible differential diagnoses near the end of the video to rule out other possible diagnoses.
Unstuck: An OCD Kids Movie
The International OCD Foundation produced this trailer for their documentary about children with OCD. The video is remarkable because of the insight the kids have about OCD and its treatment. For example, you can see them discuss exposure therapy with response prevention here. The full video is available online from the foundation.
Coping Cat
Coping Cat is an evidence-based CBT program designed to help children aged 7-14 with social, separation, and generalized anxiety. Clinicians use a workbook to help children learn and practice cognitive reframing and coping skills. This video, produced by the Child and Adolescent Mental Health Services (CAMHS) in the UK, provides a brief introduction to the Coping Cat program.
Habit Reversal Training for Tics
An important component of Comprehensive Behavioral Intervention for Tics (CBIT) is habit reversal training, in which children learn to engage in actions that make the tics more difficult to produce. In this short video, Dr. Barbara Coffey explains this treatment.