I think it more likely that the trip from Kenya actually occurred in August 1961, shortly after BHO-II's birth at the Coast Province General Hospital in Mombasa. Ann and her newborn son flew from Nairobi to London, via BOAC Flight BA162 and then took the non-stop BOAC flight from London to Vancouver, Canada. She then traveled the 110 miles or so, across the border, to Seattle in time to start Fall Semester, night-school extension classes at the University of Washington.
The trip would be challenging for a new mother, but she was young, healthy, intelligent, and capable. BOAC was very accomodating to mothers with young children back in the 1960s. No real problem!
From the Airline Timetable Images - List of Complete Timetables, the cost of BOAC from April 24,1960 until October 1, 1962 was:
From Vancouver to Nairobi cost in Canadian Dollars: Single Return
DL 1115.00 2026.80
F 1055.50 1918.80
T 764.00 1396.00
Y 701.00 1282.60
Passanger Fares could be "FLY NOW AND PAY LATER".
Arrangements could be made whereby residents of certain areas may, on payment of a 10% deposit, travel immediately and pay the balance of fare in monthly instalments.
Passanger Information for that time frame can be found here.
Connections from Nairobi - Lusaka - Salisbury can be found here.
The BOAC World Routes Map is found here.
Departure arrival times from Britian to Nairobi are found here.
Departure arrival times for London and Vancouver are found here.