The NSPCC has this page with tools and advice for how to keep families safe.
Thinkuknow for parents and carers
CEOP’s Thinkuknow Parents and Carers site features advice to help keep children safe online, and to deal with any problems that crop up.
Internet Matters is an industry backed website with internet safety resources for parents.
Parent Zone has lots of articles, videos and advice for parents looking to support their children online.
The YoungMinds parents helpline is for anyone who is concerned about the wellbeing of a child or young person.