I second Estes Park. I absolutely loved it there and we visited in August.

Look up Snow Mountain Ranch in Winter Park.

PP here, I always kept a bottle of this for visitors with altitude sickness, you might want to pick up a bottle. It may be a placebo but altitude sickness can ruin a trip so for $10 it's worth a shot. http://www.amazon.com/gp/aw/d/B000Q3BZOQ?vs=1

Anonymous wrote:OP here. Is it realistic to do a Denver-Mesa Verde-Great Sand Dunes - Denver loop? Map tell me it's 7 hrs-4hrs-4hrs driving, but is there much to see in between?

Pagosa springs is a nice place to stop, about 2 hours from Mesa Verde, Durango is a nice mountain college town. There will be plenty of stops you can make for funky little towns and wildlife viewing. I would plan a few days for the loop. I find driving in low traffic situations to be very relaxing after commuting in DC but your kids might not. The Royal Gorge is fun too, I went as a teen, though they had to do some rebuilding after a forest fire.

OP here. Is it realistic to do a Denver-Mesa Verde-Great Sand Dunes - Denver loop? Map tell me it's 7 hrs-4hrs-4hrs driving, but is there much to see in between?

My Dad and siblings still talk about Mesa Verde - I was only one so I don't remember our Four Corners trip. Also the road to Ouray.
I spent a few days visiting a cousin in Evergreen, we drove to the top of Mt. Evans (way to get quick altitude sickness but awesome) and did a day trip through Rocky Mountain NP from east to west. The drive from Grand Lake back to Evergreen was a lot less exciting. RMNP is terrific, I would set up a base in Estes Park or Grand lake (which would be quite a bit cheaper)

Lots of great scenic train rides in Colorado as well:



http://www.colorado.com/co/attractions-entertainment/trains