This is not going to be an immediate answer to breaking down the brick wall, just a few thoughts which may help.
Do you have the witnesses names from the marriage entry? Could they be of any assistance.
What did Thomas & his wife choose to call their children - possibly named after parents??
What did Thomas do for a living? - following in his father's footsteps??
Have you looked in Kea burial registers for the burial of any other Holland family members. Their names could be useful. Holland does not appear to be a common name in Cornwall, judging by the IGI, so if you find any Hollands buried in Kea, they could be linked.
If you think that the family moved to Kea when Thomas was very young, are there any other Hollands who were baptised in Kea or surrounding parishes?
And there is always the possibility that the enumerator got it wrong - check the parish register around the time of Thomas's birth, just to be sure.
FamilySearch site includes a member submitted record of a Thomas Holland baptised in Stoke Damerel, Devon in 1802, don't know if that will be of interest.
There are 45 entries for people with the surname Holland in the 1841 census for Cornwall (from the FamilyHistory online site) - unfortunately I'm down to only about 6p credit on my voucher, so I can't check them out (all 45 would cost about £3.15). However, you could eliminate some of them as being Thomas's family. These are the names (that's all you get free):
A HOLLAND 1 entry
Agnes HOLLAND 1 entry
Ann HOLLAND 3 entries
Ann HOLLAND 1 entry
Charity HOLLAND 1 entry
Edward HOLLAND 2 entries
Eliza HOLLAND 1 entry
Elizabeth HOLLAND 8 entries
Ellen HOLLAND 1 entry
Hannah HOLLAND 1 entry
Harriet HOLLAND 1 entry
James HOLLAND 2 entries
Jane HOLLAND 2 entries
John HOLLAND 4 entries
Maria HOLLAND 1 entry
Mary HOLLAND 4 entries
Philip HOLLAND 1 entry
Richard HOLLAND 1 entry
Samuel HOLLAND 2 entries
Thomas HOLLAND 2 entries
William HOLLAND 5 entries
Hope these help.
Nell