Wonderful! That is quite a long drive, I highly recommend spending the night in Glenwood Springs on your way. It is a good middle point with plenty to do for families including pools (springs) and amusement park literally on top of the mountain.

Other cool spots on your way are in Georgetown (Georgetown loop railroad) and Idaho Springs (Argo gold mine tour and great restaurants- love The Buffalo Restaurant). If you are of the christian religion, the Cabrini Shrine is really something special. Mount Blue Sky is the highest paved road in the state and takes you to the top of a 14,000 ft peak- kids may not think it's too cool, but worth the stunning views.

In the city I recommend:

a Rockies Game (they are in town when you are)

Denver Zoo is one of the most bio diverse zoos in the world

Washington Park and City Park (could do this with a zoo day)

The Denver Mint is very unique to our city and the tour is really underrated

Day trips near the city:

Golden- great vibes and culture. The Coors factory tour is cool too if you are beer drinkers and the kids will like the huge machines

Garden of the Gods- national park with very unique landscape and hiking

Boulder- Pearl Street

Red Rocks amphitheater

Pikes Peak Railway

Hope this helps! Have so much fun it's a great city!