Resources

For Parents:

Common sense media (nonprofit focusing on helping children and adolescents thrive in the world of media and technology):
https://www.commonsensemedia.org/screen-time
Help Your Kids Reduce Screen Time and Move More:
https://www.nhlbi.nih.gov/health/educational/wecan/downloads/reduce-screen-time.pdf
Screen Time Chart: https://www.nhlbi.nih.gov/health/educational/wecan/downloads/screen-time-log.pdf
Tools to monitor and manage access on your children's personal devices:
If using Apple devices running IOS 12 exclusively, Family Sharing and the new Screen Time feature can be configured to control content and time, as well as to review use. For more information, see: https://support.apple.com/en-us/HT208982
There are also a variety of services that may provide a higher level of monitoring and control that are device agnostic. You can read more about this on DigitalTrends.com - "Best Parental Control Apps for Your Kid's Smartphone"
https://www.digitaltrends.com/mobile/best-parental-control-apps/

For Teens: