Oh, one more I haven't seen anyone mention: Kate Seredy. She wrote a small series about a couple of pre-and-during-WWI-era Hungarian kids. (The Good Master & The Singing Tree.)

Also many other books, one of which was a mythologized retelling of the founding of Hungary (The White Stag), another of which was a horse-and-WWII-book. (The Chestry Oak, with an uncontrollable-except-by-the-protagonist horse. Also, he's a prince. The kid, not the horse.)