It's going to take far more than the reading of one book to take in the breadth and scope of Greek and Roman history, but I think you'll find Helene Guerber's writings a fascinating introduction to the main players and events. Helene Guerber was a well-respected scholar of her day and wrote histories of many of the nations. You'll meet her again in a couple of months when you read the story of the Hebrews. The chapters are very short and manageable for young listeners, and although children younger than 8 will likely be able to follow them, there is a lot of violence that was a part of its time that you may not want to introduce to their sensitive natures. I loved how it helped me to put familiar names and events into their proper place and helped me see the overall sweep of their histories. 

Paperback 5.5x8.5 476 pp.