I've canoed the stretch from Clearwater to Monticello.  Bring your bass stick!  Pretty nice run.  I did not pay any attention to campsites though since it was just a one day fishing trip.  I guess since we saw nobody else on the river, camped or paddling, that says it doesn't see a ton of use.  I think it was a weekday in early Sept. though.  

We easily did that stretch in a day with lots of time to fish, including driving up and back from the SW Twin Cities and the obligatory car shuttle to pick up the vehicle from Clearwater at day's end.

There's no major rapids along that stretch.  Just a few riffles and runs.  You'll have no problem negotiating them with a 6-year-old for a bow paddler.