An major difference is that Liesl von Trapp, the one who sings "Sixteen Going on Seventeen," does not exist in real life. Her real-life counterpart is Rupert von Trapp. One more difference is that ...

“Charmian Carr played the oldest Von Trapp child ... I Am Sixteen Going on Seventeen. The actress later wrote two books about her experience - Forever Liesl and Letters to Liesl - and frequently ...