There are lots of things to do at Petit Jean, it is our favorite of all the Arkansas State Parks. The hike to the waterfalls can be a little strenuous, but then we have done it with a three year old and he walked the whole way. The waterfall area is beautiful and at certain times of the year is low enough to get up close to it. The park also offers a Junior Naturalists program for the kids. It teaches them about native animals specific to Arkansas and the particular park.
We usually camp at State Parks, so this was our first time to camp at a campground. While we missed the trees and shade of State Parks, this campground made up for it in the amount of amenities. It had a pool (it was winter when we were there so we didn't actually swim, but it looked nice with ice floating on top), continental breakfast, and nice hot showers. The owners were very friendly and accommodating. I would definitely stay there in warmer weather.