I went to Krause Springs (pronounced Krau Sea) with some friends and had a blast. You can spend the day for $7 or camp overnight for $14. It isn't a hiking destination as much as a swimming/sunbathing destination. The rope swing is fun and there are some rock cliffs you can jump off of as well. The water was a little chilly, but tolerable.
Short walk downhill to a swimming hole fed by a beautiful, lush waterfall. There is also a rope swing that the kids (and maybe some of the adults) couldn't get enough of. Little caves beneath the waterfall were also interesting. The waterfall is spring-fed, so the water is always cold, no matter how hot it is outside. The kids also enjoyed playing inside (yes, inside) the trunks of the towering bald cypresses by the ridge above the waterfall. And for non-hikers, there's even a swimming pool up above that is fed by the same spring water and has a nice overlook onto the swimming hole.