Thank you Pam. I've reviewed my files and apologize for having provided incomplete details - in fact, "died in child-birth" was actually incorrect information.
I hope this isn't too confusing as both James's mother and step-mother were named Margaret. Here goes.
James appears at age "4 mos." in the 1851 census for 50 High Street, New Pitsligo in the parish of Tyrie, along with his father Robert, his sister Fanny and Robert's wife Margaret, born Banchory-Ternan, Kincardine.
I had assumed this to be his step-mother Margaret [Christie] Forsyth but have since noted that . . .
the 1861 census, shows the family living at Tillyeve, a croft or estate in the parish of Udny and lists "Margaret C., born Old Deer, Aberdeenshire" as Robert's wife.
It appears therefore, that James's mother [Anderson] was still living when he was 4 months old and she was born in Banchory-Ternan. Might she have returned there to her family if she was very ill and in need of care? I understand women often returned home for delivery of a child - perhaps she did die in childbirth as her grandaughter alleges but the child came after James.
Alternatively, and more likely, perhaps the family had already moved to Udny before she died.
Thanks so much for helping me sort out this puzzle.
Jack