"Under the greenwood tree, who loves to lie with me
And tune his merry note unto the sweet bird's throat?"

If I remember correctly, I was five or six years old and the occasion was a session of the Ottawa Music Festival, which puts the date in the spring of 1960 or 1961.

The Festival was a local music competition that formed the learning experience of many a budding classical artist -- most notably the pianist Angela Hewitt, who swept the field in the keyboard classes throughout her youth.