I acquired some books as a child from Scholastic Books. I think, if the dim past is correct, you would place an order from a flimsy catalogue. This could have been a free book from RIF though; I do not know.
All The Children Were Sent Away isn't a very good book. It's not as exciting or good as Ian Ian Serraillier’s Escape from Warsaw (also called The Silver Sword, although I didn't know that until I was an adult). I imagine I picked this/ purchased this because of Miss Shull, our fourth grade teacher, who read aloud Escape from Warsaw, and another book, Searcing for Shona by Margaret J. Anderson. Both of these were World War II books; Searching for Shona even had a similar plot - girl sent to Canada to escape the Blitz. Only Searching for Shona was the other side of that coin - what happened when the girl got to Canada. All the Children is more of the story of how one girl gets to Canada, and a little bit of what happens when she gets there.
It didn't hold my attention as much as when I was a kid, although when Ernie, the Cockney boy (oh, those awful Cockney accents; I hate trying to read them) calls Lady Drume "me old tulip" I distinctly remember thinking that phrase was a riot when I was 10 years old.
My rating: 2 of 5 stars
This is a book I really loved as a kid, but upon re-reading it as an adult, it wasn't so good. I think I probably chose it (from a Scholastic book catalog in the late 70s/early 80s I'm sure) because our fourth grade teacher had read aloud Escape From Warsaw and Searching for Shona, both World War II stories, and I probably wanted to read another one. I don't know about Searching for Shona (I haven't read it in 35 years) but Escape From Warsaw (also known as The Silver Sword is a much, much better book (I re-read it every few years or so). This book is a mere supplement, I think.