When I viewed this as a child
40-ish years ago, when it came on tv, our parents used to let us stay up and watch The Sound of Music pretty much every time it aired.
My childish mind, viewing the wedding, used to think that the nuns were singing "How do you solve a problem like Maria?" right at her wedding! I used to think "Oh my how mean, at her wedding!".
I think, about the 4th or 5th time I saw this, after suffering in silence at that part, I vocalized my sadness to my mother, and she laughed and explained that it was a song played for our benefit not an "at the wedding" scene.
What a relief!