re: Colorado, One Week with kids itenerary (flying in)

If you can, fly via Colorado Springs rather than Denver. It's a more convenient and peaceful airport. Cheyenne Mountain Zoo just west of the city is a
great smaller zoo. If you do loop through Denver the Natl History Museum is kid friendly, and there is a big zoo.

You might want to hold off on the 10,000 ft mountain tops for a couple of days while you get used to the higher altitudes. In June the mountains will still be cold.