That Westin is pretty nasty, unless they refurbished it recently, and I won't share what we found in our bed, this is a family board. I would stay away from Downtown, it gets very congested and it really isn't all that safe, especially at night.
The World of Coke and the Aquarium are great. I would recommend the Pimberton Place Pass, it might save you more. If you collect My Coke Rewards, you can get free tickets to World of Coke. Check for possible Corporate discounts for the Aquarium, alot of larger companies offer them. CNN offers tours, we have been wanting to do one, but haven't. Zoo Atlanta is alot of fun. We haven't tried the City Pass, because we get other discounts that don't make it a great option for us, but it might be for you. Check their website, they have different options to build what you want with it, including Braves games.
Your son might enjoy Six Flags, but it's quite a disappointment after years of traveling to Disney and it's alot more expensive, too.
We have stayed in Buckhead, it's busy, but alot safer than Downtown, also Lawrenceville and Buford, they are close to Downtown, but nicer and safer. And Atlantic Station, they have alot going on there as well as being a nice area and lots of restaurants. Check them out at
www.atlanticstation.com and they have a very active Facebook page for events. There is a nice Marriott: Atlanta Airport Marriott Gateway, it's really nice and has great rates, it's close to the airport if you're flying, infact, you can take the Skytrain right to it, it has great room rates and packages.