Part of YouTube's system for reporting sexualised comments left on children's videos has not been functioning correctly for more than a year, say volunteer moderators.

They say there could be up to 100,000 predatory accounts leaving indecent comments on videos.

A BBC Trending investigation has discovered a flaw in a tool that enables the public to report abuse.

But YouTube says it reviews the "vast majority" of reports within 24 hours.

Reporter: Elizabeth Cassin

Video journalist: Alex Dackevych

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