What's wrong with Harry Potter or Twilight or ________?
Every person is responsible to listen to what the Holy Spirit is telling them that they should or should not do. The Holy Spirit may not deal with every person the same way. He may expect more from some than others because of the position they hold or because of what God wants to prepare them for. The Nazarites in the Old Testament were an example of people who had to live to a higher standard than a normal Israeli. The priests and the high priest were other examples. The Bible can and should also be a guidebook to light our way and help us to make the proper decision.
The two series that were mentioned were championed by many adults because they got kids reading. The down side of the two series are that the first, Harry Potter, promotes characters who are attending a school for witchcraft and sorcery to become wizards and the latter series takes what by all accounts is a good love story and uses vampires as the characters.
Witchcraft and sorcery are condemned in the Bible. There is no gray on this issue. God's people are commanded to avoid these people completely and if those who practice these things don't turn to Christ and repent are specifically mentioned as being condemned (Deut. 18:9-12; Gal. 5:19-21; Rev. 21:6-8). Vampires, at least when I was a kid, were portrayed badly. The Count Dracula of early Hollywood fame may well have been taken from Vlad III Dracula who was a thoroughly despicable leader hundreds of years ago whose favorite method of killing seemed to be impaling people on spikes. In any event, the vampire myth is just that - a myth. It is appointed unto men once to die, and after that the judgment (Heb. 9:27). There simply isn't any place in the spiritual world for vampires or any of the other monsters of Hollywood to exist. The monsters among the living are bad enough.
These two series of books seek to make things that are bad appear good and appealing to kids. That is their danger and why I have discouraged my kids from reading either one. I haven't been entirely successful, but I have at least made my opinions known.
I'm not in favor of any censorship of any kind and would never seek to have books banned for any reason. But as a Christian parent, I do try to keep certain influences away from my kids while I am still directly responsible for them and to teach them what the Bible says about these things. There are many other series of books that kids can read that are much better. The Left Behind or the Kid's Left Behind series comes to mind first, but there are a host of better books out there that would be better for them, including our text at hand - the Bible.
There is a tremendous pressure exerted by the world to change what God has established as His truth. When the judgment day comes, when Christian's works are judged for good or bad, or at the Great White Throne judgment for the wicked dead, your works or your life isn't going to be judged against what you and your friends and society in general thought was right or wrong. You are going to be judged against what God has said was right and wrong.
The promises that the Bible holds for our salvation are written along with the scriptures telling us what is right and wrong. You simply can't pick and choose among them. You may not agree with all of them. You may not understand all of them. But God really doesn't care. They are His standards for conduct and they aren't going to change just because man moves further away from Him.