We stayed in Longleaf campground at Congaree National Park for a stop-over on our way back north from a family trip in Florida. The campsites at Longleaf each had a fire ring and picnic table, and were pretty good sized. The key thing to know about Longleaf is that you need to be prepared in several ways:

1. You have to make a reservation online. The ranger at the visitor's center told us to make sure we had some kind of documentation of our reservation. Reception can be spotty, so printing your reservation ahead of time might be a good idea.
2. There is one parking lot, and you'll be walking with your stuff into your campsite. It isn't far, but be prepared to carry things. (Note: The walk into Bluff campground is further than Longleaf)
3. There is no potable water at either campground. Bring your own. (Relatedly, there are only vault toilets at the campground)

We stayed in campsite 6 at Longleaf, which was great. Campsites 1-3 are closer to the lot, but also closer to the walk that everyone takes from their cars to their sites. For a little more space/privacy, opt for campsites 4 and above.

Although the campground is barebones, it had everything we needed and made for a great stop for us. Most of the park trails were underwater when we were there after a recent flood. It seemed like paddling would have been an optimal way to see the park and surrounding areas, but even so, we had a great time. There were lots of people out on the boardwalk trails, including lots of kids and dogs. Before you hit the trails, stop in the Visitor's Center and pick up the interpretive brochures on the types of trees/wildlife - they have kid versions and grown-up versions. Both were helpful in understanding the unique environment of the floodplain.