Backbone State Park by Strawberry Point. Even has a cave, plus a beach, the Devil's Backbone to hike, and is generally a kewl place to camp. Have taken, family, friends and Scouts there over the years.
Thanks guys. We ended up going to Big Paint in Yellow River Forest. He had a blast hiking and playing in the stream. Probably stay closer to home next time and do Palo or Backbone. He's definitely into primitive camping!
Depending on where you're at and how far you want to go, I love yellow river, but there are places closer to cedar rapids too. Pinicon ridge, nice trails and a group camp area, just checked out another one to the west of CR ,can't remember the name, along with private land,