As I have said before, i think book studies of a religious nature are good for us, as long as we are able to discern the truth of God's word. Books are written by men, and are therefore subject to false teaching, but they can still make excellent points in helping us walk closer with God as Christians. So, yes, i do book studies with my kids. Sometimes I read aloud and discuss wiht them, or if they are older I preview the book, assign readings and then we discuss. This being said, i cannot stress enough how important it is to preview EVERYTHING. Even things written by reputable men. Even they can be wrong. Compare everything to the scriptures to see if it lines up. For example: If a book tells you that being angry is sin, check out what the bible says. Anger is not sinful, it is how you handle it and the dependent on the source of your anger. That is biblical truth.
I received some of Jacob's books for next year, in the mail, and previewed them last night. I knew I had to do this because they were spiritual growth books. One is called "Don't All religions Lead to God?" Good premise, right? Yes, and for the most part, biblically sound, and staying away from salvation doctrine...until the final 2 chapters. I ALWAYS look for salvation error because so many religions teach sprinkling babies, or saying a prayer asking Jesus in your heart will save you. Well, I would point people to the scripture which does not teach either of these things. And the scripture is what will judge us. Scripture teaches that a person must beleive in Jesus as God's Son, that he lived sinless, died and rose to conquer deat, and that we must repent of our sins and be immersed in baptism for the remission of our sins, dying to our former self and pledging to live as a Christian. The bible makes all of this very clear in the gospels, Acts, and the NT letters. God is not a liar.
Which brings me to the other thing about the book that was false. The author seemed not to believe there would actually be a "hell". He stated that he doubted you could find biblical evidence for that concept, and seemed to think those not in heaven would just return to dust. Now, I would say, that I doubt he has studied scripture on the topic because the bible makes very clear that there will be eternal joy for those who are saved and eternal punishment for those who are not. Many places teach this in the NT. Not sure how he missed it, but I know I didn't miss it and we will not read those chapters of the book without an open bible so the truth can be shown and noted in margins.
Preview everything they read to see if it meets your family's standards. You will make mistakes as we all do, but do your best to guard hearts and minds. We are the product of what we see, hear, read, and experience. And so are our children. Brig them up in the Lord, as He commands, to the best of your ability.