Clingman's Dome may be under repairs. Check their website for more info.
Definitely do Cade's Cove and if you go very early, you'll see wildlife and have less traffic. Our favorite time to go is Sunday morning and arrive around 7:30-8 am. We can take our time to see all the old buildings and the mill. There's even some old time church singing at one of the churches with fiddles and guitars. We always pack a brunch or breakfast to take with us so we can do the Cove in leisure.
Any waterfall up an easy trail is a must for the girls. Shoot a lot of video.
Our grandchildren loved spending a day at Dollywood.
On the NC side you can see the massive dam at Fontana lake and take a tour boat ride around the lake. You can learn a lot of history about that area from the tour boat guide.
There's an enjoyable train ride on the Great Smoky Mountain Railroad in Bryson City, NC.
http://www.gsmr.com/