"American Mirror: The Life and Art of Norman Rockwell," by Deborah Solomon, was published in November.
In a statement released by the Norman Rockwell Family Agency, family members said they found at least 96 factual errors in the book, that the author misused sources and made "highly selective" use of Rockwell's own autobiography "My Adventures as an Illustrator."
Messages left for Solomon through her publisher Thursday were not immediately returned.
Rockwell, who lived in Stockbridge, Mass., illustrated more than 300 covers for the Saturday Evening Post. He died in 1978.
The family, in its statement, referred to one passage in the book in which Solomon describes how Rockwell went to schools at recess and stopped little boys on the street, and that such behavior might be seen as problematic in today's world.
The passage ignores Rockwell's own explanation in his autobiography that after he persuaded a boy to pose for an illustration, they would go together to ask the child's mother for permission, the family said.
"She supports this unfounded claim with another phantom theory, that Rockwell was a closeted homosexual," the statement read. "To link pedophilia and homosexuality in this way is offensive and clearly homophobic."
In an interview in October with The Wall Street Journal, Solomon, who also authored biographies of artists Jackson Pollack and Joseph Cornell, was quoted as saying she did not believe Rockwell had homosexual relationships in his life, but added that he preferred male company and that it was possible to discern "enormous homoeroticism" from his work. She said she was not attempting to speculate on his psychology.
The author did not understand Rockwell as a person, the family said, and dismissed suggestions that he was lonely, moody or frequently depressed.
"This is absurd. He did not mope, was not a chronic depressive, or a hypochondriac. He went through his trials and storms as we all do, but he was someone who ultimately affirmed life," read the statement signed by Rockwell's son, Thomas, and granddaughter, Abigail.
The family also said it was troubled that the Norman Rockwell Museum, located in Stockbridge, had endorsed the book.
In an Oct. 11 news release announcing an upcoming appearance by Solomon, Laurie Norton Moffatt, the museum's director, called the book "a well-researched and written biography that presents many unique theories and interpretations about the artist."
In a statement provided to the Berkshire Eagle, the museum said it was a center for academic freedom and for scholarship about Rockwell's life and that "American Mirror" was one in a long line of books about the artist.