queen elizibeths oldest son is prince Charles
Prince Charles, the Prince of Wales and Duke of Cornwall.
Unless he predeceases her, Queen Elizabeth's eldest child, namely the Prince of Wales, will succeed her as King Charles III. If, however, Prince Charles does predecease the Queen, his elder son Prince William will ascend the throne as King William V.
As far as England is concerned there is no name: she would simply be a princess. But if the eldest son, who is always the Prince of Wales, is married (as Charles was to Diana) then she would be Princess of Wales. When the eldest son became King she would become the Queen Consort.
Her Majesty Queen Elizabeth II's eldest son, Prince Charles
Prince William is not Queen Elizabeth's son. He is her grandson. His father Charles is Elizabeth's eldest son.
He was the eldest son of King Pandu and Queen Kunti.
Methuselah
Shakespeare had only one son, Hamnet Shakespeare (1585-1596) who was perforce his eldest.
Her eldest son, Prince Charles, will succeed the throne (note spelling) upon Queen Elizabeth's death or her abdication. If Charles dies before Elizabeth then Charles' eldest son - Prince William - will become king.
The line of succession is different in every monarchy. In some societies, the eldest legitimate son became king; in others, the eldest child. In England, the eldest son becomes king, unless the King has no sons, in which case the eldest daughter becomes Queen.
Khusrau Mirza was the eldest son of Jahangir. Manbhawathi Bai, the first wife of Jahangir, gave birth to Khusrau Mirza.
Queen Victoria was succeeded by her son EdwardWhen she was queen he was His Royal Highness Edward, Prince of WalesAs king he was His Majesty King Edward VII of the United Kingdom