My kids want to read DH. Should I let them?

That is entirely up to you. I have never been the kind of person to tell anyone how to raise their children and every child is different. My mother never censored what I read, and I read some pretty racy stuff early in my life. However, I am not going to tell anyone that they should or shouldn’t allow their child to read something. It’s a matter of your comfort level and that of your child. That being said, my suggestion is for you to read the DH books first and then decide. They do have adult material in them and are for older readers. If that makes you uncomfortable, then I suggest the Dark-Hunter manga which follows the adult books, but without the adult content. They are for readers 14 and older.