That is not it. Reading certain books and watching certain movies can warp your reality and be an obstacle in your relationship with God. Heck, watching certain news casts can warp your sense of reality.
Look at the “Star Wars geeks”. They spend much of their time watching, talking about, obsessing over, etc the “Star Wars Saga”. I don’t mind Star Wars for myself (I saw Ep III last month and thought it was awful

) because it will not shake my faith and I understand its development. Star Wars does have Oriental spirituality elements which are at strong odds with Christianity.
I find it funny, or maybe I just dont see things the way you do…but can somethings be about entertainment or does religion always have to play a role?
It is knowing your child, not allowing your child to be raised by society but by you. If all you do is give your kids Harry Potter, Star Wars, the Hulk, Brittany Spears, Christina Aguilera and all the other pop culture books and “artists” and Hollywood films, you are doing you your child a grave disservice. Heck, as much as my two sons would love to live the way you descibe…they dont. I raise my children along with their father…not society. But in that sense they can see age appropiate films shows etc They also understand the Harry Potter is make believe.
Harry Potter books *may *harm a child’s spiritual development and relationship with God. By making the child less interested in God and more interested in the attractive story involving kids, wizards, flying brooms, monsters, villains, insects, exotic animals, mystery, and so on.
If your child is not interested in religion and loves Brittany Spears, wearing skimpy clothing, playing with bratz dolls, etc then maybe Harry Potter books could be a help to your kid (I am only hypothesizing) because it introduces your child into a mythical story that can draw your child away from the over sexualized reality your child is in. Then you can explain Catholicism in relation to the Harry Potter Books - a life and death struggle between good and evil, angels, demons, saints, virtue, sacraments… If a parent were going to introduce children to a fantasy book, I would choose Lord of the Rings (not the movies, the books). The Lord of the Rings books are highly pro-Catholic and are easy to related to our faith. The Lord of the Rings Books are IMHO appropriate for children who are practicing Catholics.
http://www.catholiceducation.org/articles/arts/al0160.html