My son is 3 1/2. I've been taking him since last season. My son doesn't really follow the game. He thinks it's cool to see the men running around in uniform but doesn't get the rules or the score. So, I really take him for the pomp and circumstance to see the Wreck and the band. We usually leave before halftime and go get ice cream. I watch the rest of the game on the DVR at home.
We sit on the Northeast side - section 221. It's not the best for the sun (but with a 3 year old we're not likely sitting in our seats for long stretches.) Our section overlooks the corner where the team and the Wreck come out. We also are looking over the North student section where Buzz is most often. He enjoys spotting Buzz and the antics. We walk around some and look at different things.
You didn't mention transport, but for me, getting there easy (and having a quick escape if or
when his patience runs out
) is key. We usually park in the 'ATT A deck'. It's a block from the tunnel under 75/85 (another thing he thinks is cool). Which puts you right on Bobby Dodd way a block from the stadium, Yellow Jacket alley, etc. My son gets a kick out of riding the Marta train sometimes too.