Why do many parents heavily censor what their kids read, but NOT what they watch in movies or television?

I was talking to some parents who wouldn’t let their 8 year old child read “Captain Underpants” because the book contained fart jokes. However, they had no qualms about allowing the same kid to watch “Revenge of the Sith” unedited—even though it was extremely violent.

This isn’t the first time I’ve seen this but it stood out. I’ve seen parents rally against a book that had a single swear word in it—but a movie with several swear words gets a pass from them. What’s up with that?