Since Mr. Harnick helped found Theaterworks/USA in 1961, the company has performed to millions of children annually in 49 states and Canada, assembling a repertory of 117 musicals and plays, The New York Times said.
Harnick, artistic director from the company's founding until he retired in 2000, attracted talent such as director Jerry Zaks, songwriters Lynn Ahrens and Stephen Flaherty, and writers Marta Kauffman and David Crane.
The company helped launch careers of many actors, including F. Murray Abraham and Henry "the Fonz" Winkler.
The idea for Theaterworks came about as Mr. Harnick was directing "The Young Abe Lincoln." About a year later, Harnick and a producing partner took the show to the schools, and then formed the company to produce historical plays for children.
The company's performances eventually moved from schools to theaters and its repertory grew to include original plays and adaptations of children's classics.
Harnick, who died Tuesday, is survived by his wife, actress Barbara Barrie, a daughter, a son, a granddaughter and a sister.