If they are mature enough to have their own say then they are old enough to read scary stories. I read my first scary story when I was 5 years old and I am perfectly fine. So I think tjhat it is fine if kids read scary storys. The end
Some may think that R.L. Stine designs his books aimed toward kids. But to me it's older kids for example those who are nine to twelve years old. Even than it should be up to the discretion of the parent. There is no way kids younger than this should read his books, he is still a horror writer and very young kids could be quite scared by some of his works.
R.L. Stine has had a long and controversial career as the author of the popular "Goosebumps" horror series for children. There is debate over these books, to the point that some of his novels have been banned from the shelves. However, these books teach children to confront their fears, which is useful especially at a time in a child's life when everything seems scary.
I grew up reading R.L. Stine, and so has my son. Most of us our taught early on what is real and what is fiction. We usually have a very good understanding that while some of these things can happen, it is strictly for entertainment purposes and is a work of fiction.
Reading is important to a child's education. They should be allowed to read books by R.L. Stine. There is nothing in those books that are inappropriate for children mostly because they are works of fiction and partly because they were written for children's enjoyment. I don't see any reason why children shouldn't be allowed to enjoy R. L. Stine's books.