How much "off time" do you think you will have? Will you have a car? Depending on how much time you have and what kind of transporation you will be using, here are some suggestions:
Georgia Aquarium- just opened this past Novemember. Incredible, but VERY crowded. (Think of WDW in peak season!

) You would need to make reservations and purchase tickets in advance especially for the weekend. You can do that on their website.
http://www.georgiaaquarium.org/ Located downtown.
Imagine It!: The Children's Museum of Atlanta- not the best children's museum I've ever been to and might be "too young" for a 10 year old. Here's their website.
www.imagineit-cma.org Located downtown.
Atlanta Ballet's production of Peter and the Wolf at Atlanta's Fox Theatre- this is a one hour production designed for children.
http://www.atlantaballet.com/new/fs_performances.htm (We will probably go to this. DD8 is obsessed with ballet!)
Atlanta Botanical Garden- If the weather is nice this is a good place to spend a couple of hours.
www.atlantabotanicalgarden.org Piedmont Park is also right nearby and is a large park where you can have a picnic or just run off some steam. Located in Midtown.
Atlantic Station- this is a new development in the Midtown area with shopping, restaurants and a great movie theatre.
www.atlanticstation.com
Viriginia Highlands- this is a great little neighborhood of "boutique" type stores and neighborhood restaurants. If you have a few free hours in the afternoon it would be a good place to "hangout". There is a cute bead shop
http://www.atlantabeads.com that your DD might like to make a necklace or bracelet at.
Let me know if you have any other questions or need other suggestions. I have a DD6 and DD8 and live "intown" so I'm pretty familiar with finding things to do.
Mary