Hi Liddicoat,
On the 1841 census there is a Thomas Foster born abt 1836 in the civil parish of Harberton, registration Totnes.
Harberton Village
Thomas Foster age 35 occ ag. lab
Susannah Foster age 40
John Foster age 13
Louisa age 7
Thomas age 5
All born in county
In 1851 Thomas is a lodger in St. Austell pob transribed as Storferton looks like Harberton, also one of the other lodgers is a Richard Bennett is he a relative of Thomas wife?. So this looks like the same Thomas who is on the 1841 census, but you will need to get his marriage certificate to confirm fathers name.
This looks like John Foster in 1851
Civil parish Harberton
RD Totnes
John Foster head age 23 widow? occ ag lab born Harberton
Susan Lamsin g/mother age 77 pauper born Diptford? Devon
Further down the census page is
William Lamsin head age 44 occ ag lab born Harberton
Hannah dau age 13 born Harberton