Out of all his Sound of Music siblings, Nicholas is closest with Charmian Carr, who played older sister Leisl. The two have remained very good friends over the years, and they feel like real siblings.
When he auditioned for The Sound of Music, Nicholas had just been in a skiing accident, so in addition to having his arm in a sling, his two front teeth were missing. He still won the role of oldest son Freidrich von Trapp.
He lives in Australia.
Nicholas is the son of British actress Eileen Bennett.
Nicholas is 6 foot (1.83 m) tall.