Things to do in Knoxville?
DH is from Knoxville, so I've visited there a few times. It's been a few years, but my kids loved their zoo (especially the children's play area, and the orange - from the dust - elephants). Dollywood was a big hit with ds1, but he was a bit older than your kids when we went there.
hmm....except for our overnight trip to Gatlinburg, I'm drawing a blank on other activities. I know my MIL has taken us to some neat places. Is a day trip to the Smoky Mountains practical for you?
I'll try to remember what else we've done on visits there.