They've also gained a wide adult audience, in addition to the younger readers.
I am an adult reader of the Harry potter. Even though the audiences for it is not limited to people of my age group. It  attracted a wide adult audience as well as younger readers
I like reading. Harry Potter is one of my favorites Ah, cool. Did you know they were written by J. K. Rowling? Yes, it's such a long, intricate story. I'm blown away by her accomplishment. Her books  won multiple awards, and sold more than 400 million copies. That's astounding!
They have attracted a wide adult audience as well as younger readers, and are often considered cornerstones of modern young adult literature.