>the privilege of being sent to the country during a dangerous time.

Children of all social classes were evacuated- the slum child evacuated to a prosperous country farmhouse is practically a trope, while some children of wealthy families stayed in London. The only thing that decided whether children went or not was their parents' choice.

Though the Pevensies are relatively privileged in that they have a (EDIT: family friend not uncle) in the countryside who has room for them rather than being sent to a stranger's house.

(EDIT: actually, I can't remember- is there an indication that they knew the Professor before the war?)