I love the Colorado Springs area! We were talking about going there this summer, but with the fires and with some family things happening we changed our plans. I haven't been there with my kids, but I remember going as a kid. The Cheyenne Mountain Zoo is great and Santa's Village is fun too. There are some things for kids at Garden of the Gods too. There is also a lot to do in the Denver area and in Rocky Mt. National Park. We used to stay at YMCA of the Rockies for family reunions and had a great time!
There are tons of fun things to do in SD Black Hills and a lot of fun places to stop on the drive from Sioux Falls to Rapid City--the Corn Palace in Mitchell, the Akta Lakota Musem in Chamberlain, Wall Drug. There are lots of kid friendly things to do in Rapid, Keystone, Hill City, and the Mount Rushmore area. I've never stayed at a resort area there, but have known people who stay at a plane that I think is called Hart Ranch. I would caution that the Black Hills in August can be really tricky when the Sturgis Rally is going on--lots of motorcycle traffic, crowded restaurants and attractions and no place to stay.
The Twin Cities area has a lot of fun too. We love the MN Zoo, Como Park Zoo, the Mall of America, the MN Children's Museum. If you go towards the end of August there is also the state fair and the Renaissance Festival. There are also several other museums, some GREAT kids' bookstores, lots of parks, and several swimming beaches. I don't know of any resorts, but there is a hotel that has the Waterpark of America.
We took our kids to Chicago a couple of years ago and had a blast! There are two great zoos, a couple of great children's museums, the Museum of Science and Industry, the aquarium, Navy Pier, and lots of other attractions. There are also good swimming beaches on the lake. I don't know of any resorts though. We just stayed in a hotel near the airport. It was cheaper than staying closer to the city, but did mean a little more time in the car each day.
Send me a message if you want more details. I lived in SD for 11 years so I can tell you a lot more about that area. I've been to Chicago 6-7 times. We live in Rochester, MN and spend quite a bit of time in the Twin Cities and I lived there for a year, too so I can give you more info about that area and the Rochester area.