Violent video games
The major problem with video games is not the content by itself. The ESRB rating means nothing if it can be sold to virtually anyone who is tall enough to put their money on the counter. Pass and ENFORCE laws prohibiting the sale to minors (such as liquor or cigarette sales) and the problem lessens greatly.
Granted, you can't totally shield kids from blood and gore. Look at the evening news as an example, or the movies that kids attend. When a movie is rated PG, just how many parents take the time to investigate the reason for the rating- or do they just use the theater as a built in baby sitting service? The theaters are just as guilty by letting the kids in.