It’s actually pretty hard to do lockdowns because there’s been so much consolidation. Many parents can turn on the built in controls, but then they face problems like “do you block YouTube entirely, even though their homework will include links to things like videos from NIH hosted there?”
The big problem isn’t that kids could innocently find sexual content but also that grownups will try to trick them into engaging with things for a variety of reasons. This is different from letting your kid have free rein of the public library because the library didn’t have some guy recruiting for a political movement putting books in the children’s section and the librarians wouldn’t let that creepy dude hang out there.
This came up at a school party recently where multiple parents of first graders were talking about how quickly YouTube will go from auto playing LEGO and Minecraft videos to some pretty unhinged stuff.