If you google "張玉鳳的兒子,張南子", you would find a picture where 張玉鳳 was standing with a man about 50 years old who was called "張南子". In this picture, the young boy is also called "張南子"(The young man looks quite similar to the Mao at the painting "Mao went to Anyuan Mine". But the picture was created not based on Mao himself but just a picture only.