I do believe, if I was the librarian, I would take a few moments out of my busy day and sit down with the child and talk to him/her about the book. Maybe this kid is doing this on a dare from other kids, or maybe he has an older sibling who asked him/her to get it for them, maybe this kid is very curious and needs some guidance. What's wrong with asking the question, "Why are you interested in this book?".