Addy by Connie Porter (1994, Paperback)

I bought these books for my six-year-old, and she really enjoyed them. I think she read the entire series in less than a week, and has read through them a couple times since then as well. I read them myself, because they were written when I was a teenager, so I had never read them before.
The main character, Addy, is a slave at the beginning of the series, but after half of her family is sold to another plantation, she and her mother run away to freedom. But Addy discovers that even with freedom, life is hard. Money is tight, and even in the North people are prejudiced. And throughout the series, Addy wishes for her father and brother and baby sister.
It is a very moving story, about freedom and family and love. It is very well-written. I highly recommend this series, for anyone, but especially for little girls. It's a great way to get kids interested in history.