From the 1943 Warner Bros. classic cartoon, Yankee Doodle Daffy. A, yes, sleepy-looking kid duck with a big lolly that just sits there as his agent, Daffy Duck (voiced by Mel Blanc) furiously pitches him to Smeller Productions president Porky Pig (also voiced by Mel Blanc). Daffy claims he can play the banjo, also.
At the end, the kid finally lets loose with a deep operatic baritone (singing voice by Billy Bletcher), singing "In the Garden of My Heart" from 1913.
"Sleepy Lagoon" is a 1930 instrumental that turned into a popular standard after lyrics were added in 1940. It was also the name of a 1943 film, and the nickname of a local swimming hole in California where a murder sort of led to the zoot suit riots of the 1940s.