Hi,
For clarity: The following records show on Ancestry’s Scotland Select Births & Marriages. All spelling as found.
John McFadyen married Margaret Stirrat 29 Dec 1813, Stevenston Ayr.
Robert, son of John McFadyen and Margaret Stirrat born 16 Apr 1815 Greenock East, Renfrewshire
Mary McFadzen, daughter of John McFadzen & Margaret Sterrat born 21 Apr 1817, bpt 4 May 1817, Kilwinnig, Ayr
Not sure about the following census, it might be of later use if only for elimination purposes – it’s the only one I can find with a suitable Robert who is a Tailor!
http://www.freecen.org.uk/cgi/search.pl1841 Census - Gorbals –Lanarkshire, Rutherglen Loan
Robert McFadyen, 30, Tailor, not born in county
Ann McFadyen, 25, not born in county
Mary Ann McFadyen, 2 months, born Lanarkshire
They share this address with Francis McBryerty, a labourer & his wife Helen, both born in Ireland, and their two children aged 2 and 1 day respectively, both born Lanarkshire