I was 11 years old in 1967 when the senior campers at my Jewish summer camp (Camp Ramah in the Poconos) mounted a magical production of SOUTH PACIFIC, all in Hebrew of course. I was smitten. That same year I saw my first show on Broadway, FIDDLER ON THE ROOF then starring Harry Goz.
(There's sort of a theme here--I lived in Israel in 1971 when I saw the first class HaBimah mounting of THE ROTHSCHILDS, also in Hebrew. Somehow they duplicated John Bury's dazzling Bway set design for that production--wow!)
But of course, movie musicals were a major part of my wonder years anyway: WEST SIDE STORY in '62, MY FAIR LADY in '64, MARY POPPINS in '64, THE SOUND OF MUSIC in '65, OLIVER in '68. Bway musicals were no mysterious thing by the time we actually got to our first Bway outing.