ACROSS THE nation, numerous adult readers continue to get in a tizzy about their kids’ picture books.

In 2013, Jeff Smith’s fantasy/adventure graphic-novel epic “Bone” was among the works that received the most complaints and requests for restricting or de-shelving, according to the American Library Association’s annual “State of the Libraries” report published Sunday. And for the second straight year of knicker-knotting, the book series that most got quite a few grown-ups’ undies in a bunch was Dav Pilkey’s “Captain Underpants.”

“Bone’s” offenses? Political viewpoint, violence and racism, the ALA reports. And “Captain Underpants’s” crimes against wee humanity included “offensive language” and material unsuited for its target demographic.

” ‘Bone’ has been challenged numerous times over the years, and I’m grateful to all the librarians, educators and patrons who’ve spoken out in support,” its creator tells The Post’s Comic Riffs.

“After observing challenges to ‘Bone’ for a while now, I’m starting to think that the reasons given to have it removed say much more about the people who want censorship than they do about the books themselves,” continues Smith, who is on the board of the Comic Book Legal Defense Fund.

“Racism, really? What book did they read? It wasn’t ‘Bone’! It makes me very glad to be part of the CBLDF’s efforts to protect the freedom to read.”

Of his “Captain Underpants,” Pilkey said in a statement he was surprised “that a series with no sex, no nudity, no drugs, no profanity and no more violence than a Superman cartoon has caused such an uproar.”

“Kids love the books, and fortunately most parents and educators do, too,” added Pilkey, noting that the report’s complaintants represent a small minority.

The list, of course, can partly be a function of what’s popular. Both “Bone” and “Captain Underpants” have been distributed by Scholastic, which is a publishing pipeline to schools.

A challenge, the Associated Press reports, is a “formal, written complaint filed with a library or school requesting that a book or other material be restricted or removed because of its content or appropriateness.” There were 307 challenges last year — a significant decrease from 464 a year earlier.

“The list shows the wide range of books that can get people rattled and touch upon their deepest fears and antagonisms,” Barbara Jones, director of the ALA’s Office for Intellectual Freedom, told the AP.

Also topping the list were: Toni Morrison’s “The Bluest Eye” (crimes: language, violence, sexual content; Sherman Alexie’s “The Absolutely True Diary of a Part-Time Indian” (sexual content, racism, references to drugs); EL James’s “Fifty Shades of Grey” (you know why); Suzanne Collins’s “The Hunger Games” (violence); Tanya Lee Stone’s “A Bad Boy Can be Good for a Girl” (sex and drugs); John Green’s “Looking for Alaska” (drugs and sex); Stephen Chbosky’s “The Perks of Being a Wallflower” (drugs and gay sex); Rudolfo Anaya’s “Bless Me, Ultima” (sex and Satanism, plus language).