it's completely unsurprising that a child raised with no spiritual grounding would be interested in a book that teaches how to live and attempts to answer the questions that rationalists and atheists have nothing satisfying to say about.

How does one live a good life? Every religion tries to answer that question. Has the GP sufficiently replaced religion with something else to help their child answer that question?

One life is too short and too permanent to figure it out from trial and error so we have an instinct for myth to help guide us. That's why religion evolved.

You can help your child navigate that problem and separate doctrine from the helpful parts, or try to shelter them from scary ideas. Good luck with the latter strategy, especially if you want them to have a relationship with you as adults.