Thanks for that. I have actually looked at the original parish register, which says that Peter Hogg was born 'in adultery', and at the Kirk Session records which have literally pages and pages and pages of details about the case of Robert Hogg and Janet Finlayson's illegitimate child.
Robert Hogg was a married man, living in Dunipace at the time, and Janet Finlayson lived with her parents, though, infuriatingly, the Kirk Session records do not name either her father or her mother, referring to them merely as 'Janet Finlayson's father' and 'Janet Finlayson's mother'! So in spite of reams of detail, none of it helps to find out who Robert's and Janet's parents were.
I rather doubt that there are any other children of this couple to be found.
There is a family tradition that Robert Hogg was related to James Hogg, the 'Ettrick Shepherd', but in the absence of any evidence, other than the same story being prevalent in two branches of the family separate since the early 1800s, I have to treat this with some care.
Peter's son James, my gggrandfather, was in the same household as Janet Finlayson, aged 60, and George Finlayson, aged 50, in the 1841 census. I have not found any trace of either Janet or George after that date.
Best wishes and thanks