Interesting post (from a while ago, I know) at Monica Edinger's blog about children's books of the century. It's in response to a Guardian article from even longer ago, about defining literature of the 20th century.
I think if I had to pick . . . well, I'm not sure what I would pick for some decades.
1900s - ??
1910s - Anne of Green Gables, although that always seemed to epitomize late-19th century Canada. But apparently it was published in the teens, and has to be counted. Contemporary lit is nothing like historical-looking-back, after all. I'm sure it's a topic for countless theses, what Montgomery's remembered late-19th century Prince Edward Island says about 1910s Canada.
1920s - ??
1930s - The Little House books, Laura Ingalls Wilder, another historical-looking-back. (Okay, they were partially published in the 40's, too, but let's not be lazy here.)
1940s - ??
1950s - The Lion, the Witch, and the Wardrobe, by CS Lewis
1960s - Harriet the Spy, Louise Fitzhugh. Also Charlie & the Chocolate Factory by Roald Dahl. I love that both these titles have some subversity to them.
1970s - Judy Blume . . . either Forever or Are You There God, It's Me Margaret
1980s - ??
1990s - Harry Potter. Who else? It was like a gigantic bombshell, hitting a children's lit market gone stale and sleepy.
And now another question. Why is it that so many greats of children's lit are fantasy, which by adulthood has been relegated to the paperback stacks of dateless dweebs, at least in popular imagination? And a number of the others are historical. Why do so many amazing books take kids to another place and time, whether real or imagined?
This would be a really cool children's lit/history seminar.
Suggestions for the missing decades welcome! Or even additions to the ones filled.