Dozens of authors swarm the National Mall this weekend for the National Book Festival, including “Goosebumps” author R.L. Stine.

For the past 20 years, “Goosebumps” series author R.L. Stine has been writing the stuff of nightmares: Tiny hamsters turn evil! A teacher develops an appetite for children! An old camera snaps photographs that predict the future — in a nightmarish way! Even the famous “Goosebumps” logo — rendered in bright green slime — is spooky.

It turns out that Stine himself (known as “Bob” to family and friends) has quite a genial personality and a great sense of humor. He’s also a big fan of the National Book Festival, simply because “it’s such a thrill to see all these people who are interested in books.” As he has in past Book Festival appearances, Stine will write a ghost story with young readers, share a ghost story from his own childhood and sign copies of his books — including his latest, “Goosebumps Most Wanted #1: Planet of the Lawn Gnome.”

I was one of those kids who started reading “Goosebumps” with your very first one in 1992. I was 9!
That’s nice! My readers grew up. It came as a horrible shock to me at first. No one told me!

I think it came as a horrible shock to us, too.
I’m on Twitter. When I talk about how it’s the 20th year of “Goosebumps,” everyone writes, “I feel so old.” They’re your age. How do you think I feel? But it’s a great thing; I’m very proud of it.

Why do you think your books had such an impact on readers?
I think everyone likes a good scare. Adults like to be scared, and kids like to be scared if they know they’re safe at the same time.

Is there a certain type of kid your books seem to resonate with?
When I started out doing the scary books, we assumed that the readers would all be girls because everyone just assumed girls read and boys don’t. The early ones were pretty much aimed at girls. And then the fan mail started coming in, and half was from boys. We were really surprised. One of the real secrets [of “Goosebumps”] is that it was the very first series ever that was equally divided between boys and girls for its readership. To this day, when I do the Book Festival, you’ll see the line for autographing; it’ll be half and half.

Stine has written his second horror novel for adults, “Red Rain.”

Has the audience reading your books changed?
Kids are a lot more tuned into things, and there are a lot more devices that are important in their lives. But as far as kids go, I don’t think they’ve changed. And luckily for me, fears don’t change at all. Well, I guess you can have the fear that your iPhone is going to run out of power. I have to write that one down. That’s a great plot.

What can you learn from an R.L. Stine book that you never could from, say, Judy Blume?
Nothing. The books are strictly reading motivation. They’re strictly to show kids that you can pick up a book and be really entertained, so I don’t have any moral lessons. I just want them to say, “Gee, this is really fun. Maybe I’ll try reading this [new] book now.”

Is it true that you never start a book without a title?
Every book starts with a title: That’s how I get the stories. I had this title, “Little Shop of Hamsters.” And I thought, “I love that title.” So then I started thinking, “OK, how do I make hamsters scary? What if there’s this weird pet shop and all they sell [are] hamsters? What if there’s a giant glass hamster cage with hundreds of hamsters and what if a kid gets trapped inside one night?” That’s how the book started.

You just wrote your second adult horror novel, “Red Rain.” What’s it like writing for adults?
It was the opposite of writing these books for kids. When I write a “Goosebumps” book, I want to make sure the readers know it couldn’t happen; it’s not real. But when you write for adults, every detail has to be real or they’re not going to believe it.

Will you be writing more for adults?
I don’t know. “Red Rain” comes out on Oct. 9. All my followers on Twitter grew up with “Goosebumps,” and they all say they’re looking forward to “Red Rain.” They were begging me, “When are you going to write something for us? Please write something for us.” That’s why I wrote it — to try [to] reach my old readers.

National Book Festival, National Mall, between 7th and 14th streets NW; Sat. 10 a.m.-5:30 p.m. and Sun. 12-5:30 p.m., free; 202-485-9880. R.L. Stine’s appearances: Presentation at Family Storytelling Stage, Sat., 12:20-12:40 p.m.; presentation at Teens and Children, Sat., 4:25-5:10 p.m.; signing, Sat., 1:30-2:30 p.m.