Butterfly Pavilion, Denver Zoo, Downtown Aquarium, The Children's Museum, Six Flags Elitch's, the play area at the Cherry Creek Mall, the play structure at Washington Park, the public library downtown, Museum of Science and Nature, Red Rocks Amphitheater, the Colorado Railroad Museum (if your kids are into trains at all, this is a must!), ice-skating at DU Ritchie Center, Heritage Square in Golden, Downtown Golden, Coors Brewery (for the grownups!). THEN there's all the stuff you can do up in the mountains. Denver and the surrounding areas are VERY kid friendly. We lived there for 13 years. My oldest was almost 12 and my youngest was almost 7 when we moved. Every summer, I would make a list of all the things we wanted to do that summer in and around Denver. In all those years, we never completed everything we wanted to do. I'm jealous you get to go visit. Colorado's awesome. Have fun!!