The Walnut Canyon National Monument is about 10 miles from Flagstaff, Arizona. Our family visited the canyon in April. It was a very windy day but we still had an enjoyable time. The weather was comfortable otherwise. The monument is about a 1 mile loop that descends into the canyon.
800 years ago, the Sinagua people called this home. As you walk the trail, you will see the cliff dwellings along the sides of the canyon where they used to live. The kids really enjoyed exploring some of the dwellings. They learned about the native plants and the crops that the Sinagua people lived on. My son participated in the Junior Ranger program which required him to complete several pages of a workbook, answering questions about the park. He had fun completing the packet and getting his badge at the end of our journey.
I'd recommend visiting the canyon if you have kids that don't mind climbing a lot of stairs. The path in is easy as you're going down several flights of stairs but once you complete the loop, you'll need to climb back up and that could be tough for smaller kids. My kids were at 9 and 12 and they handled it fine. My daughter even challenged me to a race back up. We were pretty tired once we reached the top, and yes, she won.