In reply to your query re Gilbert McKenzie and family of Saltcoats. I have some information in regards to Gilbert b. abt 1778 Isle of Arran married to Mary Dobbs of Ireland b abt 1797. They are noted on the Rev. Landsborough Parish list in Stevenston/Saltcoats for the years 1819/1822/1836. Gilbert noted as a sailor.http://www.ayrshireroots.com/Genealogy/Records/Census/1820s/...
There is no mention of a child named Charles. They are found again on the 1841 census as well as the 1851 census and again, no mention of Charles.
After a search last night I can find a Charles McKenzie married in Stevenston to Mary McKinlay 1844.
My interest in the family is in regards to their daughter Janet McKenzie born 1840 Stevenston.
She married Hugh Stevely 1859 Stevenston and their second son is named Gilbert McKenzie Stevely.
Best wishes in your search