Bill Finch was pretty close on his memory of the Tex Avery cartoon which
featured this song. Those of us here in Cartoon Network Land (Atlanta)
who have 'toon watchers (children) will remember the "rest of the story."
The cartoon features an owl family in which the "papa", who has a rich
European accent is a music instructor. He is teaching his young son (and
other children) vocal lessons. The piece seems to be very boring and the
young lad spontaneously breaks out in his "Sing-a" piece - clearly
preferring jazz to the classics. This really upsets the old maestro who
ends up kicking the kid out.
The boy heads off to town and passes a local radio station which is
holding auditions for a talent show. Most of the contestants are dumped
via a trap door until the boy and "Sing-a" are discovered. They prep the
kid and he steps up to the microphone and starts singing.
The papa shows up and the boy panics and reverts to the tired old tune
that his instructor father had been teaching him. Just before they dump
the kid down the chute, the papa runs in and encourages the lad to "go on
and singa- about the moon-a and the June-a and the Spring-a"! A lesson
in flexibility in parenting, I'm sure.