My DD4 loves learning about history. Go to museums. On a trip recently we asked DD if she'd rather go to a dinosaur museum or a museum about the French and Indian War. She thought hard and said, "Well, I really don't know enough about the French and Indian War. Let's go there."
I think my DD loves the narrative. History is just a bunch of stories with common themes. She loves the biographies as well. And, she just loves the who, what, when, where, and why's of war.
She memorized the president in their order when she was 2.5, and those guys served as great stepping off point for American history. She was also naturally interested in Greeks, Romans, Egyptians, and American Indians. It is kind of flashy history, you know? NASA's history was also fun.
I am all for little bits of exposure over time. Just follow their interests. (Like, I am pretty sure my DD's eyes would glaze over if I started reading a book about the Industrial Revolution, but to each their own.) We really just read about history, answer her questions, let her ramble about it, and occasionally visit a museum.
