What to say to little kids about why you don't want to read a library book

My four-and-a-half-year-old daughter loves reading and going to the library. I let her go through the picture books and choose what she wants to read, but every once in a while she'll want to check out a book on a topic that I think is too mature for her (alcoholic parents, remembering the Holocaust) or isn't in line with what our family believes. (The latest one in that category was about how Allah is happy when little girls wear the hijab.)I used to get out of reading them by telling her, "I think that's for bigger kids," but now that I've started reading her chapter books, I don't think she believes me. I'm curious what other people tell their kids in this situation. I'm usually trying to watch her toddler sister at the same time and don't have the time or energy to go into a long explanation. Thanks. via /r/Parenting http://bit.ly/2wqkFnH