YouTube hosts thousands of disturbing videos featuring promotional images from popular children's characters, according to recent analysis.

Some of the videos were targeted at children on YouTube. Many of the videos tap into popular keywords.

YouTube says it screens videos to pull inappropriate ones from its children-oriented YouTube Kids app, and encourages people to flag any videos they view as inappropriate on its platforms.

But writer James Bridle, who highlighted the problem in a recent Medium post, said that the way the company's site is designed, it actually encourages the production and posting of such videos.

Parents who let their kids watch YouTube unattended might want to pay closer attention to what they're viewing.

YouTube is serving up to kids thousands of disturbing videos, many from obscure producers, that are sprinkled in with kid-friendly ones from well-known studios, according to analysis in a recent Medium post and past reporting from the BBC. At first glance, the inappropriate videos can be hard to distinguish from the benign ones, often involving well-known characters and themes. But they can often be violent or involve abuse to kids, and many appear to be generated automatically and cheaply in an apparent attempt to profit off the sometimes indiscriminate tastes of younger kids.

"The architecture [that Google and YouTube] have built to extract the maximum revenue from online video is being hacked by persons unknown to abuse children, perhaps not even deliberately, but at a massive scale," wrote writer and artist James Bridle, who took to Medium on Monday to help sound the alarm about the continuing phenomenon.

In a statement to Business Insider, YouTube said that while it is looking out for younger viewers, it's trying to keep its site as open as possible.

"We're always looking to improve the YouTube experience for all our users and that includes ensuring that our platform remains an open place for free communication while balancing the removal of controversial content," a YouTube representative said.

Peppa Pig's disturbing trip to the dentist

One video Bridle highlighted as "controversial" that hasn't been removed is a knockoff video of Peppa Pig, a popular animated character in the UK. The BBC first reported on the disturbing video in March. Posted to YouTube last year, the clip looks and sounds similar to a real Peppa Pig video and even involves a similar situation - going to the dentist.

But the knockoff video is punctuated with the disturbing sound of a child wailing in the background. When Peppa gets to the dentist's office, he injects her with a green serum and proceeds to pull out all her teeth. She then has to fight a sinister-looking masked monster. Needless to say, the real Peppa Pig's dental visit isn't nearly as horrifying.

That's just one of many disturbing pseudo-Peppa Pig videos on the site, Bridle said.

"Many are so close to the original, and so unsignposted - like the dentist example - that many, many kids are watching them," he wrote on Medium. "I understand that most of them are not trying to mess kids up, not really, even though they are."

But bogus Peppa Pig clips represent a small portion of the disturbing kids videos that can be found on the site, Bridle noted. There are thousands of other videos that may not show disturbing content per se, but are upsetting nonetheless, because they appear to be automatically generated based on popular keywords and tuned specifically to attract kids' clicks, according to Bridle.

"There are vast, vast numbers of these videos," Bridle said. "Channel after channel after channel of similar content, churned out at the rate of hundreds of new videos every week. Industrialized nightmare production."

It's unclear what motivates users to post the disturbing content to the site. Last year, in an attempt to discourage these types of videos, YouTube began pulling ads from videos that depict kids characters engaged in inappropriate behavior, removing the ability for the creators to monetize them.

YouTube Kids may be designed for kids, but it's not a guaranteed refuge from inappropriate videos

YouTube recommends that parents direct their children to its YouTube Kids app. That app, which regularly garners more than 11 million weekly viewers, is designed to offer kid-friendly content aimed at audiences aged 13 and under.

But disturbing videos have infiltrated the YouTube Kids app as well. Parents have reported that the app has shown videos of popular animated characters dying in a car crash, others of popular characters urinating on each other, and one of a real child apparently bleeding after her forehead was shaved, The New York Times reported.

A YouTube representative told The Times that videos uploaded to its site are automatically scanned to see whether they are appropriate for its Kids app and monitored after they are posted. The company also encourages parents to alert it to videos that are inappropriate for YouTube Kids. YouTube representatives review such videos and can remove them.

Fewer than .005 percent of the videos on YouTube Kids were removed in the last 30 days because they were inappropriate, the company representative told The Times. "We strive to make that fraction even lower," the representative said.

Yet despite YouTube's efforts, there are still plenty of creepy, kid-targeted videos on its sites. And it doesn't appear to be all that hard for kids to find them.