This series of books published by Scholastic and written by Ann McGovern (among others) is a great resource on a variety of topics. Some of the books include:
...If You Lived in the Days of the Knights
...If You Lived with the Sioux Indians
...If You Lived in Colonial Times
...If You Lived in Williamsburg in Colonial Days
...If You Lived 100 Years Ago
...If You Sailed on the Mayflower in 1620
...If You Grew Up with Abraham Lincoln
...If you Grew up with George Washington
...If you Lived at the Time of the Civil War
...If you Lived at the Time of the Great San Francisco Earthquake
...If you Lived at the Time of Martin Luther King
...If you Traveled West in a Covered Wagon

REVIEW
My children and I have enjoyed these books. The illustrations are not out of this world but the content is really great. The authors present the information in a question style, "How were the knights dressed for battle?", "How would you send a letter?". We found lots of fascinating information in these books presented in an easy to digest format. Older children can read these books independently. Younger children will enjoy being read to from them. If you are doing a history unit I would definitely look to see if any of these '...If You Lived' books were written for your topic. They are a great resource for a variety of ages.