The father's delicacy of health kept the mother much engrossed; the elder girls were therefore appointed as little mothers to the younger children, and it was to his eldest sister, Elizabeth (afterwards Mrs.Dundas), that the young Charles always looked with the tender reverence that is felt towards the earliest strong influence for good.
From the first he had one of those pure and stainless natures that seem to be good without effort, but his talents were only considered remarkable for arithmetic.

His elder brothers used to set him up on a table and try to puzzle him with questions, which he could often answer mentally before they had worked them out on their slates.

His father died in 1830, after so much invalidism and separation that his five-year- old boy had no personal recollection of him.

The eldest son, Mr.Forbes Mackenzie, succeeded to the estate of Portmore, and the rest of the family resided in Edinburgh for education.

Charles attended the Academy till he was fifteen, when he was sent to the Grange School at Bishop's Wearmouth, all along showing a predominant taste for mathematics, which he would study for his own amusement and assist his elder brothers in.
His perfect modesty prevented them from ever feeling hurt by his superiority in this branch, and he held his place well in classics, though they were not the same delight to him, and were studied rather as a duty and as a step to the ministry of the Church, the desire of his heart from the first.