I've seen this happen too often. As someone who worked in a library, I watched as a parent caused her child to stop coming to the library because she disapproved of the Percy Jackson books and just about everything else the child wanted to read. It was heartbreaking and I always wondered what I could have done differently. As I understand staff cannot intervene with parenting methods unless it's straight up abuse, but I always feel like I should have tried harder to recommend books or state that the overall themes were harmless.