Ah I hadn't thought of the railway!
Unfortunately David drops off the records after 1841; I think he dies in 1849.
I'm still trying to verify his children, the only one I know for sure is:
Robert (born 1809 in Scotland), who notes his da as a porter at his marriage.
James (born 1826 Liverpool)
John (born 1827 Liverpool)
The baptisms I'm *almost* sure are for both of them don't show an occupation..
I think there was also Andrew, born 1811 Liverpool, but I'm still checking that!