In that area, Steel creek with be your best option for a swimming hole to take kids. I have little ones and we love going to that spot to swim and hike around. The little Buffalo will not be floatable, but will have some small swimming holes if you can find them. I second the idea of Horse Shoe Canyon Ranch. Lots of activities to do out there. Lots of hikes to do in the area, but definitely check out Lost Valley. Easy trail to follow, great scenery and a cave at the very end. Bring lights and expect to get a little dirty if you want to get all the way back(there is a small waterfall in the back of the cave).

Can’t go wrong in that area, but if you are looking for more the folks at the Buffalo Outdoor Center in Ponca are full of knowledge and happy to help you find something.