The 1841 census shows them in Scott's Close, Dalkeith:
James Howatson, 25, labourer
Elizabeth Howatson, 25
Willimina (sic) Howatson, 1
Thomas Howatson, 20, plasterer journeyman
All are born in Midlothian
I suspect the Howatsons may have had some children who died young between censuses.
Thomas may well be a brother, so worth chasing up to see who his parents are.
The ages are, of course, rounded in 1841.