Amy Stender is 31 years old. But when it comes to reading, she prefers to embrace her inner child.  She chooses books written for kids half her age. 

"The story and the themes behind it are very adult and universal. They are very simplistic but yet very complex, all at the same time," she said.

A study found 55 percent of buyers of young adult books are over the age of 18.  

"I used to talk a lot more with teens about teen books and now I'm sort of talking to everyone about teen books," said  Shannon Peterson, president of the Young Adult Library Services Association.

Peterson says gateway books like Harry Potter, Twilight and the Hunger Games first gave adult readers permission to browse the kids section and they haven't left since.

"I think it's awesome," said Peterson. "I think there's amazing, amazing books out there for readers as young as eight and I think it's wonderful that more adults are seeing that and appreciating that."

Literary Agent Kristin Nelson sees this as part of a larger trend today: the blurring of the lines between what appeals to adults versus kids.

"I can listen to the same music that my teenage nieces and nephews listen to," she said. "There are adults who play video games. There's less of a distinction between, oh this is only for adult readers and this is only for kids."

Nelson says publishers are paying attention to their expanded audience, and are now actively marketing to adult readers with ads in popular magazines and in movie theaters.   And many big name adult authors have also gotten in the game, including John Grisham and David Baldacci.

"This is a hugely growing field, as we know, but also very competitive. So the quality of literature that's being published as young adult titles is, is pretty phenomenal," said Peterson.

But with so many adults picking up kids books, is there a concern that authors will start slipping in adult themes?

"They shouldn't be writing with that audience in mind, because their true audience are the young readers and that's the only people they need to satisfy with their stories," said Nelson.

Strender says she's found some real literary treasures between the covers of kids' books and hopes others will give them a try.   

"If you look beyond, you know, the demographic age on the book you can definitely open up your mind and your, your reading habits to a lot more options out there," she said.

And more evidence of the blurring of the lines between entertainment for adults and kids: the Young Adult Library Services Association just put out a list of books written for adults that have special appeal to teens as well.