There is a wealth of information available to support parents and to help keep children safe online. The following list is not exhaustive but should provide a useful starting point:

This is a recently published video by financial times films, it gives an important insight to the impact of social media on our children and our family life. The 15 minute video is well worth a watch!

https://www.youtube.com/watch?v=6UY2HOpuTlk

ChildNet International: resources for young people to raise awareness of online safety and how to protect themselves. 
http://www.childnet.com/ 

Digizen: provides online safety information for teachers, parents and young people. This is a branch of the Childnet site above http://www.digizen.org/

Internet Matters: provides help to keep children safe in the digital world.
https://www.internetmatters.org/

Think U Know: resources provided by Child Exploitation and Online Protection (CEOP) for children and young people, parents and teachers.
https://www.thinkuknow.co.uk/

Help and advice for families in a digital world
https://parentinfo.org/

Help for parents on how to keep their children safe online
https://www.internetmatters.org/?gclid=EAIaIQobChMIktuA5LWK2wIVRYXVCh2afg2aEAAYASAAEgIJ5vD_BwE

Parent Zone has teamed up with National Cyber Security Centre (NCSC) to create CyberFirst Navigators - helping young people understand how to stay more secure from online threats (such as scams and hacking). A number of useful resources are available to download on their website: https://parentzone.org.uk/article/cyber-security

Practical advice for parents, teachers and governors on protecting children from extremism and radicalisation.
https://educateagainsthate.com/

NSPCC advice for parents
https://www.net-aware.org.uk/

Independent reviews, age ratings, & other information about all types of media for children and their parents
https://www.commonsensemedia.org/

CEOP Exposed Film (Sexting/sharing images/information).

These are a series of short films that might help you understand why children might send inappropriate selfies and what to do about it!

https://www.youtube.com/watch?v=9uJOXOAQ9Qo

Understanding Why
https://www.youtube.com/watch?v=XjV0lKYpakk&feature=youtu.be

Talking to your child
https://www.youtube.com/watch?v=qSIyExhWg6M&feature=youtu.be

When should I be worried?
https://www.youtube.com/watch?v=E5LA2nKHVZ0&feature=youtu.be

Where to get help
https://www.youtube.com/watch?v=IK3TDzETkRg&feature=youtu.be

https://www.childline.org.uk/info-advice/bullying-abuse-safety/online-mobile-safety/sexting/

Home Office advice on healthy relationships, including sexting and pornography

https://www.disrespectnobody.co.uk/relationship-abuse/what-is-relationship-abuse/

Information about bullying online – what to do!

Childline
https://www.childline.org.uk/

NSPCC: Bullying and cyberbullying
https://www.nspcc.org.uk/preventing-abuse/child-abuse-and-neglect/bullying-and-cyberbullying/

Digital wellbeing guide and advice for parents
https://www.saferinternet.org.uk/blog/digital-wellbeing-–-guidance-parents