It allllllll depends on what kind of kids they are and what they are into. Aquarium is cool.....google things to do in ATL. THere are events, shows, festivals, etc all the time. You could almost take them to White Water or 6-flags for about the same price as aquarium I believe. Prices have went down a ton and there are deals at like banks and stuff to get the tix even cheaper.

Have fun and GL! =)