The below link will take you to the National Online Safety website where you can download a wide variety of guides.
You can also find information from NSPCC and O2 via the following links:
https://www.net-aware.org.uk/
This page allows you to search for apps, social media sites etc to get the latest information and guidance. It is updated regularly.
https://www.o2.co.uk/help/nspcc
This page has all the information about the partnership between NSPCC and O2. The tools and tips section has lot of useful information and there is information on a helpline for parents at the bottom of the page.