Ok, here's all I've managed to collect.
John Hogg, b. Abt 1813, Ireland. Fireman
Helen Cairns, b. Abt 1811, Ireland. Domestic Servant
Children:
Mary b. Abt 1839  Ireland
William b. Abt 1841  Ireland
Agnes b. Abt 1843  Ireland
Henry b. Abt 1845  Ireland
Elizabeth b. Abt 1847  Ireland
As there next son James was born Ayrshire, Scotland, presumably they left Ireland between 1847 and 1848.
I've found a small mistake with Helens name on an IGI record, where it states she was Helen Cains.
Finally, on the 1861 Census, they appear to have 2 children named Agnes. 1 at 18yrs and the other at 11mth. A mistake? Perhaps a relative they brought up as their own daughter? I'm guessing it's not a common thing? Any ideas?
TIA,
Alan.