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Thousands of videos on YouTube look like versions of popular cartoons but contain disturbing and inappropriate content not suitable for children.

If you're not paying much attention, it might look like an ordinary video featuring Peppa Pig, the cheeky porcine star of her own animated series. But soon after pressing play on this particular YouTube clip, the plot turns dark. A dentist with a huge syringe appears. Peppa's teeth get pulled out. Distressed crying can be heard on the soundtrack.

Parent and journalist Laura June almost immediately noticed something was not quite right as her three-year-old daughter was watching it.

"Peppa does a lot of screaming and crying and the dentist is just a bit sadistic and it's just way, way off what a three-year-old should watch," June says. She wrote about her experiences on the website The Outline.

"But the animation is like close enough to looking like Peppa - it's crude but it's close enough that my daughter was like 'This is Peppa Pig.'"

It's far from an isolated case - BBC Trending has found hundreds of similar videos of children's cartoon characters with inappropriate themes. In addition to Peppa Pig, there are similar videos featuring characters from the Disney movie Frozen, the Minions franchise, Doc McStuffins, Thomas the Tank Engine, and many more.

Some of the videos are parodies or have such over-the-top content that they're clearly meant for mature audiences. Others are unauthorised copies of authentic cartoons or use the characters in innocent ways - troubling to copyright lawyers perhaps, but not necessarily harmful to children.

However many, like the video Laura June's daughter saw, both contain disturbing content and can pass for the real cartoons, particularly when viewed by children.

Image copyright SmileKidsTV/YouTube Image caption Some of the cartoons feature violence or frightening situations

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Hundreds of these videos exist on YouTube, and some generate millions of views. One channel "Toys and Funny Kids Surprise Eggs" is one of the top 100 most watched YouTube accounts in the world - its videos have more than 5 billion views.

Its landing page features a photo of a cute toddler alongside official-looking pictures of Peppa Pig, Thomas the Tank Engine, the Cookie Monster, Mickey and Minnie Mouse and Elsa from Frozen.

But the videos on the channel have titles like "FROZEN ELSA HUGE SNOT", "NAKED HULK LOSES HIS PANTS" and "BLOODY ELSA: Frozen Elsa's Arm is Broken by Spiderman". They feature animated violence and graphic toilet humour.

The people behind the account didn't respond to Trending's request for an interview. We attempted to contact several other producers of similar videos - and got the same result.

How to avoid inappropriate videos on YouTube

• The YouTube Kids app filters out most - but not all - of the disturbing videos.

• YouTube suggests turning on "restricted mode" which can be found at the bottom of YouTube pages:

Image copyright YouTube

• The NSPCC also has a series of guidelines about staying safe online, and there are more resources on the BBC Stay Safe site.

Image copyright CandyFamily/YouTube

Trending also contacted two companies behind the cartoon series being ripped off, Disney and EntOne - the distributor of Peppa Pig. Neither wanted to comment.

So should parents take more care when it comes to allowing their children to watch cartoons on YouTube?

Sonia Livingstone is an expert on child online safety and professor of social psychology at the London School of Economics,

"It's perfectly legitimate for a parent to believe that something called Peppa Pig is going to be Peppa Pig," she says. "And I think many of them have come to trust YouTube... as a way of entertaining your child for ten minutes while the parent makes a phone call. I think if it wants to be a trusted brand then parents should know that protection is in place."

"I don't think we want to police it for the whole world," Livingstone says. "A lot of this material is satirical, creative - or actually offensive but within freedom of expression. What we need is child protection."

Image copyright CandyFamily/YouTube

YouTube did not offer a spokesperson for interview, but in a statement said: "We take feedback very seriously. We appreciate people drawing problematic content to our attention, and make it easy for anyone to flag a video.

"Flagged videos are manually reviewed 24/7 and any videos that don't belong in the app are removed within hours. For parents who want a more restricted experience, we recommend that they turn off the Search feature in the app."

The company also suggested that parents use the YouTube Kids app, which is available for mobile phones and tablets, and turn on "restricted mode" which limits flagged content. It can be found at the bottom of any page on the YouTube site, but cautions that "no filter is 100% accurate".

And since Trending began investigating, several of the channels that we brought to the attention of YouTube have been removed - including the one containing the video of fake Peppa visiting the dentist.

Blog by Anisa Subedar and Will Yates

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