Heather Menzies-Urich, left, with other “Sound of Music” cast members Kym Karath, center, and Debbie Turner in 2015. (Kevork Djansezian/Reuters)

Heather Menzies-Urich, an actress who played one of the singing von Trapp children in the hit 1965 film "The Sound of Music," died Dec. 24 in Frankford, Ontario. She was 68.

Her son, actor Ryan Urich, told Variety that the cause was brain cancer.

Ms. Menzies-Urich played Louisa von Trapp, the third-oldest of the seven von Trapp children, in the film adaptation of the Rodgers and Hammerstein musical that starred Julie Andrews and Christopher Plummer.

"The Sound of Music" captured five Academy Awards, including best picture.

"Heather was part of 'the family.' There is really no other way to describe the members of the cast of the movie of 'The Sound of Music,'" Ted Chapin, president and chief creative officer of the Rodgers and Hammerstein Organization, said in a statement.

A Toronto native, Ms. Menzies-Urich also appeared in the films "Hawaii" and "Piranha." On television, she appeared as a fugitive in "Logan's Run" and had guest spots on "Dragnet," "Bonanza," "Marcus Welby, M.D." and other series.

Heather Menzies-Urich (as Louisa) at center, and the other von Trapp children sing 'So Long, Farewell' in a scene from 'The Sound of Music.’ (Silver Screen Collection/Getty Images)

Survivors include three children, several grandchildren and a great-grandchild.

Her husband, actor Robert Urich, died in 2002. After his death, she established the Robert Urich Foundation to raise funds for cancer research.