I don't think he was born until later in 1851 - so after the census?
Births, September 1851
Neath district vol 26, page 535
Voakes, Henry
1861 census, Reference RG09, Piece 1679, Folio 132, Page 12
Hallatrow, High Littleton, Somerset
Weeks, George Head M 66 Coal Miner b High Littleton, Somerset
Weeks, Hester Wife F 51 b Paulton, Somerset
Vokes, Henry Grandson M 10 Scholar b Neath, Glamorganshire
Vokes, Sarah Granddaughter F 3 Scholar b Clutton, Somerset
Jenkins, Edward Grandson M 6 Scholar b Westbury, Gloucestershire
(presumably, Westbury-in-Trym?)