If you can only do one activity in Chattanooga, this is it.
If this place were to have a drawback, this would be the sheer size of it - by the end, you might be skipping some of the exhibits because you've getting tired. Fortunately the layout gives you a lot of leeway to tailor your visit.

There is a "master path" that winds through the center of building. This alone will give you at least as much of the aquarium experience as most other places, but at almost every corner on every floor there is an extra path that takes you to a special exhibit. If you stop to view all of these you can plan on spending two or three hours inside. A nice feature of the main path is that it is on a moving sidewalk, so you can visit each exhibit and then get a short rest watching one of the huge main tanks while you are carried to the next one. If some of your party are tired or need a break, and the others want to keep going, you can also sit down and enjoy the main tank while the others go through one of the extra exhibits. This makes it a good place to take grandparents, toddlers, or others who might tire more easily than the rest of the family.

You will want to stop by the gift shop afterward. It has so many great souvenirs - the hardest part might be not buying all of the absolutely adorable plushes!

If there is a line to get in (which there usually isn't) or if your kids have some energy left to burn afterward, the area outside is a great one to play. There are things to climb on , a small stream, etc.