Disney's Silly Symphony series was winding down, as 1938's "Mother Goose Goes Hollywood" was one of the last in the series, and the last one to use the Silly Symphony title card.
As the title implies, the Disney crew transformed various Hollywood stars of the day, such as Katherine Hepburn, Laurel & Hardy, W. C. Fields, and Eddie Cantor into various nursery rhyme characters. Donald Duck (Clarence Nash) makes his final appearance in the Silly Symphony series in a brief cameo early on. It's very odd to see Charlie McCarthy used here without Edgar Bergen, though.
Fields had, in fact, played Humpty Dumpty in "Alice In Wonderland" prior to this cartoon, hence his usage here. Most of the stars were satirically depicted by other studios as well through the years, including WB and MGM.