Yeah. It's rather important to be able to tell the difference between educational books about sex, normal, healthy sexual relationships, and porn. I can understand banning porn that encourages unrealistic expectations from sex (which is a problem), and the other two. If you ban the other two, you can bet children will learn about sex from porn.
Or not at all and be really surprised when they get pregnant.
People under 18 have sex all the time, and they should absolutely be reading stuff about sex before then.