Many major attractions in Atlanta are located in downtown and are in walking distance. Atlanta also has great public transit system MARTA. You can use that if you do not have any private vehicle. Purchasing Atlanta CityPASS is a good investment. It covers 6 major Atlanta attractions and saves about 50% if you visit all 6 attractions.
Day 1: You can start your day by visiting world's largest aquarium. There are exhibits like Ocean Voyager where you can see Sharks. Cold Water Exhibit for Dolphins, Sea Turtles and Whales. Tropical Diver has colorful fishes from Amazons. There are programs available for up-close encounter with Dolphins which is fun and educational for kids.
In the late afternoon visit Coca-Cola Museum. There are variety of exhibits about the history of Coca-Cola. There is factory simulation of how Coke is made. There is a 4-D theater and you can try variety of drinks from around the world made by Coke.
Update 2018: Earlier this year we took same exact trip but since kids were little older we skipped aquarium and replaced it with The Jimmy Carter Presidential Library and Museum. It was such a learning experience, not just for kids but for us adults too. As kids got so much interested in learning about president, we bought them Passport to Presidential Libraries where they got to learn about other presidential libraries and they can get all the pages stamped as they visit other libraries. We are working on planning our other trips to these libraries now.
Since kids were already in this exploration mode, I took opportunity to get them reading little more about presidents. Hence I bought this fun coloring book about presidents. It turns out to be big hit for both kids.
Coming back to topic of the itinerary, visit Centennial Olympic Park in the evening. Fountains of Rings is fun for kids. Every 4th Saturday of the month, there are great activities for families in the park. There are two wonderful playgrounds for toddlers and young kids.
Day 2: Start your 2nd day of trip to Atlanta by visiting Atlanta Zoo. (800 Cherokee Ave SE, Atlanta, GA 30315-1440). Zoo has variety of exhibits for mammals , birds and amphibians. Lots of trees and bushes. Verity of options to view any given animals. At time of entrance they provide you events calendar for the day. So can visit any given animal during its training or feeding time and be really up-close with animals. It is a great experience.
If you are travelling with kids, Atlanta Children's Museum is a great place to visit. Lots of hand-on activities and exploration to do for the kids of all the ages, including toddlers.
Spend evening visiting Atlanta Underground (50 Upper Alabama St SW,Atlanta, GA 30303-3192) Underground Atlanta is bustling with activity, any time of the day. You can enjoy daily entertainment and shop from street vendors. You can take guided walking tours and learn about Atlanta’s past from Civil War to Civil Rights.
Day 3: Take tour of CNN Studio (190 Marietta Street Northwest,Atlanta, GA 30303-2762
) on day three. Reservation is advisable. There are some walk-in tickets but not many. It is a great experience to see how news are created in real world. You can take behind the scene tour. CNN Studio Food Court has great variety of dining options available from fast food to upscale restaurants. From pastry shops to cocktail lounges.
You can spend rest of the day visiting Georgia University , Georgia Dome and Dr. Martin Luther King National Historic Site (450 Auburn Avenue, N.E.,Atlanta, GA 30312).