Found this online listing of historical fiction by time period, but I see most of the books are recently published, I do not know their content.
http://www.historicalnovels.info/20th-Century.htmlThis short list from bfbooks.com, The Endless Steppe by Esther Hautzig set in pre-WWII Russia; the House of Sixty Fathers by Meindert DeJong set in China during Japanese invasion; No Promises in the Wind by Irene Hunt set during the Great Depression (sounds like a better option than the Grapes of Wrath- that book still haunts me). Then there's To Kill a Mockingbird. Anne of Green Gables series is set in the early 1900's.
Edited to add: there is a Young Adult page, might be better pickings
http://www.historicalnovels.info/Young- ... ovels.html