The Hattiesburg Zoo in Kamper Park is a genuine rarity in Mississippi: free admission, seven days a week. The zoo is small by major-city standards — about 30 acres — but it is well maintained and holds a decent collection of animals including giraffes, primates, and various big cats. The rides (a carousel, a miniature train) make it genuinely child-friendly in a way that larger, more serious zoos sometimes aren't.
The Zoorassic Park seasonal exhibit adds dinosaur models along the paths (check dates — usually spring through summer). The grounds are shaded and pleasant in the morning; avoid the hottest part of Mississippi summer afternoons. The zoo sits inside Kamper Park, which has picnic tables and a small lake, making a good half-day outing for families. Parking is free.