Youtube Parental Controls
New controls have been released by YouTube to give parents better filtering management. Previously the only filtering option was 'Restricted Mode' which basically meant videos flagged as 18+ were filtered out. Called 'Supervised Experience' there are now filters for:
Explore - 9+
Explore More - 13+
Most of YouTube - all videos except 18+ (the current Restricted Mode)
YouTube have released a handy explainer video to explain how to set this up.