The 1861 census shows Thomas at Tomneen, Knockando:
Thomas Robertson, 35, farmer of 40 acres employing 1 boy, born Aberlour
Julia Robertson, 28, born Knockando
Elizabeth Robertson, 3, born Knockando
Alexander Robertson, 2, born Knockando
Jane Robertson, "0", born Knockando
May Emerson, 14, domestic servant, born Knockando
James Calder, 15, cattle boy, born Rothes
The 1871 census for Tomneen:
Thomas Robertson, 45, farmer of 42 acres, employing 1 boy, born Aberlour
Julia Robertson, 38, born Knockando
Elizabeth Robertson, 13, born Knockando,
Alexander Robertson, 12, at school, born Knockando
Jeanie Robertson, 10, at school, born Knockando
Julia M Robertson, 8, at school, born Knockando
James Robertson, 6, at school, born Knockando
Thomas Robertson, 3, born Knockando
Margaret H Robertson, "0", born Knockando
Lachlan McDonald, 15, farm servant, born Aberlour
I think the children's names probably reflect their grandparents and parents - Alexander, Jane, Thomas, Julia, and perhaps Julia's parents were a James and an Elizabeth.
Thomas' age does not match the birth date of Thomas Geddes Robertson exactly, but it does seem to be him in every other respect. People were often a bit vague about their ages.