Greg Cox wrote:
Exactly. Ninety percent of movies made before 1960 or so, including most musicals, comedies, adventure films, and so on, would be considered G-rated in that they didn't contain any questionable sex or violence or adult content.
Although that was largely due to the Hays Code, which pretty much forced all movies to be suitable for family viewing. The MPAA rating system was instituted in the late '60s as a replacement for the Code, one that would allow for more adult movies to be made so long as they were labelled appropriately. A lot of movies made before the Code, in the '30s, could get a lot more adult.