Here are some resources that you may find helpful:
Talking to Children About Tragedies & Other News Events from the American Academy of Pediatrics
Helping Children Cope With Frightening News from the Child Mind Institute
Promoting Compassion and Acceptance in Crisis from the National Association of School Psychologists
Managing your distress in the aftermath of a shooting from the American Psychological Association
News and Children from the American Academy of Child and Adult Psychiatry
Explaining the News to Our Kids from Common Sense Media
American Academy of Pediatrics