YouTube is to restrict the availability of videos showing children's characters in violent or sexual scenes if they are reported by viewers.
Last week, a blog post by writer James Bridle highlighted how YouTube was still being swamped by bizarre and indecent videos aimed at children.
The site has already barred such videos from earning advertising revenue.
YouTube said its team was "made up of parents who are committed to improving our apps and getting this right".
Often it appeared that the videos had been algorithmically generated to capitalise on popular trends.
"Stock animations, audio tracks, and lists of keywords being assembled in their thousands to produce an endless stream of videos," he said.
Many used popular family entertainment characters such as Spiderman, and Elsa from Frozen, and had been viewed millions of times.
"Someone or something or some combination of people and things is using YouTube to systematically frighten, traumatise, and abuse children, automatically and at scale," he wrote.
YouTube has already barred such videos from earning advertising money when they are reported by viewers, to try to remove the incentive to produce them.
The company said it would now also give them an age restriction if they are reported by viewers, so they cannot be viewed by people under 18.