In the original script Jane was to have died (Maureen O'Sullivan wanted out of the Tarzan series). Fan protest forced a last-minute rewrite in which Jane recovers from her near-fatal wound, admitting she had been wrong to disobey Tarzan.
Johnny Sheffield claims that he was handpicked by Johnny Weissmuller after screening hundreds of applicants for the role of boy. Weissmuller is also the person who taught Sheffield to swim for the movie.
Tarzan had to "find" a son, because censors would not allow Jane to become pregnant because she and Tarzan were not legally married.