Mary Ann Clark Born 8 Jan 1882 IN St Pancras London

Parents are John Clark (b 1852) and Mary Clark(nee Trevillion - b 1855) we think she had a child around 1905/1906 called James who went on to be called James Pitt-Jones but we have no birth certificate for him, we have found a marriage certificate showing Mary Ann marrying William Jones in Inverkeithing in Scotland in 1915 and she's calling herself Clark but her child would have been born by then so trying to piece together any info as to what name he would have been registered under...then nothing until she marries Willie Killick in 1926 in London, and notes herself as a widow? Any help greatly appreciated!!