My family and I recently went to a boy scout campout at Natural Falls State Park. The park is right at the Oklahoma/Arkansas border at Hwy 412 W, West Siloam Springs, OK. I live about 25 minutes from this park and I had never heard of it. I was amazed. The park rangers are friendly and keep a close eye on the place. The campsite was very clean, I did not see any litter. They have playground equipment and lots of open space for the kiddos. They have the nature walk which has beautiful scenery and the waterfall. Although the most impressive part about the park was the clean and warm bathrooms! It was freezing the weekend we went so I was very grateful for the heated bathrooms. We just pitched a tent but there is an area for RV's. Each camp area has a pit to make a fire and a grill. There is a fee to camp there, but honestly I have no idea what it is. That information can be found here: http://www.touroklahoma.com/detail.asp?id=1+5U+3603. We had a blast there and I would definately recommend camping there.
The only thing I did not like was the teeny tiny sign they had advertising where to turn into the park from 412. I would never have found the turn in the dark, it was daytime and I still missed it.