"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 yesterday were not immediately returned.
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 behaviour might be seen as problematic in today's world.
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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 paedophilia and homosexuality in this way is offencive and clearly homophobic."
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.
In an October 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.