In 1851 William himself is a pupil at a school in Somerset.
And the Catherine from 1841 is also at a school locally.
There is only one Truss family I can see back in Reading , so it looks as if this is father, Thomas, probably with a second wife, unless Mary is known as Elizabeth or vice versa. Change of occupation too, so a few questions
Merrit Street Reading
Thomas 50 shoemaker bn Falmouth Cornwall
Elizabeth 48 bn Bucks
Maria 21
Charles 17
Betsy 15
Ann 12
Thomas 8
Susan 5
Emma Dalworth26 married daughter bn Abingdon
All other children bn Reading