According to the Hancock's Drift page on Facebook (March 2013):
There may have been other siblings, born before Thomas and Ann Kennedy, but there is as yet no certain proof of their connection. These are:
1. Alexander KENNEDY, b. abt Aug 1777; d. May 1800 (22y 9m), Fetter Lane, London; bd. 4 May 1800, City Road Wesleyan Chapel, Camden, London
2. Daniel KENEDY, b. abt Jun 1782; d. Jul 1783 (1y 1m), ?Bridge Lane (I can’t find a Bridge or Budge Lane in the Fleet Street Area, so presume it should be Bride Lane: JP),
Fleet Street, London; bd. 25 Jul 1783, City Road Wesleyan Chapel, Camden, London
3. - KENEDY, b.?, d. abt Aug 1783, Bride Lane, London; bd. 5 Aug 1783, City Road Wesleyan Chapel, Camden, London
In 1798, the Kennedy family moved to 125 Fetter Lane in the City of London, and this was Ann’s home until she was married in 1808. Charles Kennedy was a successful businessman, and Ann was well-educated. Ann Kennedy’s mother died in 1804, when Ann was 14 years old. Ann married James Hancock on 21 February 1808 at the church of St George the Martyr, Bloomsbury, London. Their first child, Charles James Hancock, was born exactly a year later and was christened at St Andrew’s (Parish) Church in Holborn, London. Of the six children Ann gave birth to in England, only three survived to make the long journey to the Cape Colony in 1820; three infants were left in Bunhill Fields Cemetery, across the road from the Wesleyan Chapel in City Road, Camden. It was for this precise reason that James and Ann Hancock made the decision to emigrate to the Cape Colony; to provide a better life and prospects for their children.
1820 Settler, part of
Hezekiah Sephton's party in the ship Aurora (344 passengers).
Departed from London on 15 February 1820. Arrived at Simon's Bay 1 May 1820.
Arrived at final destination of Algoa Bay, Cape Colony on 15 May 1820.
View of Bride Lane, off Fleet Street, showing figures and horse-drawn carriage
Thomas Colman Dibdin (1810-1893), 1851
http://collage.cityoflondon.gov.uk/collage/app?service=external/Item&sp=I%3ADibdin%2C+Thomas+Colman+%281810-1893%29%3A%3A&sp=1445&sp=X