Bertie was the seventh child of David Bertram Agnew and his wife Eliza Ellinor Hewitt. Two of Bertie's siblings are buried in the same plot of the Cartwright Cemetery.
The Agnews originated from Kinloss Ontario. After spending a number of years in the Cartwright and Holmfield districts, David, Eliza and their surviving family of seven moved to farm near Wauchope Saskatchewan. The family's story, including the children buried in the Cartwright Cemetery, is told in the local history book "Precious Memories of Time. A Salute to the Pioneers of Wauchope and Parkman" (1989).