Like you don't want to break the kids heart, so instead of telling their bulldog got run over by an American Lorry, they tell them that they were "evacuated to Canada"?
Boatloads of kids got sent overseas for protection in WW2 from the UK, so the children would have heard of that program. Do you think some of them broke the news of their best friend the family dog, in a euphemism like "he went to live on a farm"?
If a child got killed by a bomb, but they couldn't tell their kid friends their pal is dead, do you think they lied to the kids that their human friend were evacuated to Canada?
[That's the real question, the title is a cover for that one]
Just a reminder to potential respondents that, despite the wording of the question which invites you to imagine what may have been said, this subreddit does not permit speculation. Please keep answers grounded in solid and cited source material. Thanks!
It seems unlikely to be a commonly used euphemism. Regarding pets, to take a few examples from the BBC's "People's War" archives of user-submitted accounts, a more forthright attitude was common, particularly with rationing and lack of meat:
"I remember we had a pet rabbit and at Christmas seeing my Granddad kill skin and gut them, hold them open with sticks and hang them in the scullery to air them, ready for Christmas dinner. Come the New Year we would get new pet rabbits."
"Food was rationed, especially meat, so my mother would make broth with sheep's head, rabbit pie was popular because it wasn't rationed - the whole family got upset when my dad killed our pet rabbit and made it into a pie. We called him a murderer and none of the children would eat it."
If there was a story to spare a child's feelings "evacuation to Canada" would be rather peculiar, being there was no official evacuation of pets, compared to any number of simpler explanations, e.g.:
"Granny and Grandad had rabbits in hutches at the bottom of the garden. I loved them. I spent my holidays with my grandparents and as soon as I arrived I would rush to the bottom of the garden to see how many rabbits there were in the hutches. I gave them names. I would ask, 'Where's Dolly or Daisy?' favourites from a previous visit. The reply was generally along the lines of 'Well another little girl thought she would like to take care of her and we thought you wouldn't mind, we've got some more pretty little bunnies for you'. It was many years later when I finally realised that the delicious rabbit stew that Granny made for me actually came from the hutches at the bottom of the garden! I was totally unaware of what happened between hutch and table. Granny and Grandad were very discreet."
Regarding other children, less than 3,000 children were officially evacuated overseas through the Children's Overseas Reception Board (CORB), around 1,500 of them to Canada (though perhaps ten times as many travelled by private arrangement), and the majority returned to Britain shortly after the war finished; over a million children were officially evacuated within the United Kingdom, a far-flung part of the country would scarcely be less remote with wartime travel restrictions. It's hardly possible to be definitive and may have happened, but not so frequently as to be noteworthy.