Congratulations to ..... for the correct answer that there were 7 Von Trapp children in The Sound of Music. They werent all great singers so four other children were brought in to enhance the singing of the seven von Trapp children - to produce a better, fuller, more polished sound. Among the four "extra singers" was the younger sister of Charmian Carr who played Liesl. According to the British tabloid The Sun, the movie was selected by BBC executives as one to be broadcast following a nuclear strike, to improve the morale of survivors. The BBC did not confirm or deny the story, saying, "This is a security issue so we cannot comment".