Britain's media regulator Ofcom says TikTok and Alphabet's YouTube have failed to take meaningful steps to protect children from harmful content online.
Ofcom research found 73% of 11-17 year olds were exposed to harmful content over four weeks, mainly via personalized feeds.
Ofcom said both companies maintained their systems were sufficient, but the regulator disagreed.
Snap, Meta and Roblox have agreed to introduce stronger protections against online grooming after Ofcom's demands.
The UK government is urged to strengthen the law to better protect children online.
