What is the name of Mary Shelley's only surviving child?

Mary Shelley’s only surviving child was Percy Florence Shelley.

He was born on 12 November 1819 in Florence, Italy, during the Shelleys’ years abroad. His middle name commemorated the city of his birth. Percy Florence was the fourth child born to Mary Shelley and the poet Percy Bysshe Shelley, but his siblings died young.

Mary’s first child, an unnamed daughter born prematurely in 1815, survived for only about ten days. Her son William died in Rome in 1819, probably from malaria, and her daughter Clara died in Venice in 1818. These losses deeply affected Mary, and the birth of Percy Florence brought some relief after years of grief.

Percy Florence later became heir to the Shelley baronetcy after the death of his half-brother Charles Shelley in 1826. He married Jane Gibson St John in 1848 and survived his mother, who died in 1851. Some accounts also mention Elena Adelaide Shelley, a child registered by Percy Bysshe Shelley in Naples; her parentage and status remain uncertain, and she was not Mary Shelley’s surviving child. That historical complication does not change the canonical answer.