I have to put in a word for the Denver Art Museum. Having recently completed a landmark expansion (strikingly designed by architect Daniel Liebeskind), the DAM is a huge museum with something for everyone. And they have lots of excellent programming and activities for kids, so there’ll be plenty for the little one to do and see.
Winter Park is an easy drive from Denver, with lots of outdoor activities in addition to the ski resort there. I second the suggestion to check out Boulder, a hip town (which is actually more like a half hour from Denver) with a pedestrian mall (“Pearl Street”) which is second to none for people watching and window shopping.
For dining, Denver has a surprisingly good variety of Japanese restaurants (there’s an interesting history around the Japanese-American population of Denver). Check out Domo near downtown, which is a “Japanese Country” restaurant and also something of a museum of Japanese culture. If you like vegetarian food I can’t recommend Watercourse highly enough (give it a try even if veggie dining isn’t your usual thing). And Parisi (tucked away in Northwest Denver) has a nice casual not-quite-fast-food atmosphere, and some of the best Italian food this side of Florence (the owner is Florentine and the cuisine is authentic).
Be prepared to fall in love. Denver is a great town!