Children are people too FYI and depending on age, upbringing and maturity have minds that are pliable and inquisitive. These books are likely to germinate the questioning in young minds as to whether or not there is a God, and whether "God*" should be killed. It is by many critical reviews NO Lord of the Rings or Chronicles of Narnia.
*or the their projected interpretation of "God."
If you don't want your children to see a movie...don't take them to it. Sounds simple enough.