Those things are not equal. It's perfectly reasonable to take books with graphic depictions of sex and violence out of the children's section.
The bible is likely in the library and kids could reach it, and violence is acceptable to an arbitrary point which changes based on the media.
Meanwhile, kids like me were watching Sleepaway Camp at age 9 and it was fine.
But at least for young children, exposure to pornography is well-recognized as harmful. Not just morally, but psychologically. Maybe even as a form of child molestation.