Nick,

Not totally sure about kids that young (my disclaimer). There is TONS of stuff to do in Atlanta, though (I'm still 'discovering' the city.....been here since '89!)

First, look at the different events that are going on by searching:

http://atlantahappenings.creativeloafing.com/gbase/Events/index

There is always something to do. If you want to spend some time outside, try Stone Mountain, Kennesaw Battlefield or check out some of the town squares like in Marietta or Lawrenceville. Want hiking, head North to the 'mountains'. A day trip to Chattanooga (2 hour drive) is always fun with a tour of the aquarium.....

Good luck and have fun!

Steve