YouTube has a fake toons problem.

Parent groups are sounding the alarm after thousands of seemingly kid-friendly YouTube videos were found to contain violent and sexual content, in cartoons made to look like shows such as "Peppa Pig" and "Doc McStuffins."

The videos look and sound like clips from popular children's shows, so much so that parents might not recognize the problem if a child is simply watching YouTube in the background. But deeper investigation shows there are duped videos and even entire channels dedicated to these fake, adult-themed cartoons.

Many of them even slip through the filters on YouTube Kids, a firewalled version of the popular video service. In some cases, the video will feature a kid-friendly thumbnail, while the video itself might be entirely different. In other cases, the whole video might be an adult-themed copy of a popular kids' show.

"There are a number of parody sites across the range, parodying all kinds of TV shows, including children's shows," Stephen Balkam, the founder and CEO of the Family Online Safety Institute, told CTV News Channel on Tuesday. Balkam says many of these videos are expertly made to "feel" like the real thing, but they actually contain "far more disturbing content than would be suitable for young children."

For instance, the channel Super Kids TV features videos with Peppa Pig, Paw Patrol, various superheroes and characters from "Frozen," all mashed up together.

Though they may sound like a child's toy box come to life, the videos are often nightmares to behold, with lots of crying and frightening scenes involving monsters and blood. Many of these videos venture into dark territory, with the characters often being chased, attacked or injured in a bloody manner. There is very little dialogue, except for an occasional scream of "Oh my God!" dug into other seemingly kid-friendly channels such as "Fun Kids Smile" and "Smile Kids TV," only to find similar content. One video showed Mickey Mouse stepping on a nail. Another depicted Doc McStuffins, a popular U.K. character, in a sexual situation with an unwilling snowman.

Balkam said he doesn't know who is behind the videos or why they are being produced.

"Who knows what goes on in the minds of people," he said.

He points out that YouTube has a robust system for reporting inappropriate content, so parents can block sites such as those mentioned above.

However, he says there's no better preventive measure than to take the time to talk to your child. "Talk early and often about the fact that they may well come up against inappropriate content and images," he said.

More tips for educating children on fake YouTube cartoons can be found on the Family Online Safety Institute website.