Hi again,
Have found your William on 1851 census.
Barbara Smart..age47...brn Strathmiglo, Fife..
William Smart...son...age 27..brn Collessie , Fife..Ag labourer
Helen Smart...daughter..age 16..brn Collessie, fife...hand loom linen weaver
Margrt Smart..daughter..age 13..brn Collessie, Fife...scholar
John Smart..son...age 11..brn Collessie fife..scholar
they were living at Sheilds Bridge..parish of Kettle, Fife
Hope this helps,
Susan