YouTube has made parenting a fair bit easier. Not all that long ago, parents (myself included) had to work a hell of a lot harder to keep our kids entertained when we were trying to get any form of work done. Often times it means putting on a movie or a show up on your TV, but those shows would end and you would be forced to stop what you are doing to find something else that the kids wanted to watch.
Now that kids have far easier access to tablets and computers, and they all already seem to have a reasonable grasp at how to use them, kids have started to fall in love with YouTube, and parents aren't complaining. Kids can now access videos for themselves, without having to ask their parents to come over and help them. And while there is a ton of kid friendly content on YouTube, it also allows them to accidentally start watching something that they absolutely shouldn't be.
This a screen grab of the top four videos you get when you search "kids videos," and they all look (and are) perfectly harmless.
But once kids start watching videos, other suggestions of what they can watch start popping up in the sidebar, and some of them can be kind of insane.