It's free to visit the museum. Be sure to sign in at the front desk! They keep a log that tallies the number of visitors to the museum each day.
At the entrance, my kids like to check out the woolly mammoth display. Then, we head on upstairs to the second floor for the "Hands on History" play area. This area also has exhibits to check out, like covered wagons that showed what life was like for pioneers moving westward.
"Hands on History" is only open to families with children. It's not open to day care groups, which means it's generally a quiet experience. When we've been there, there have sometimes been no other visitors in the section. Other times, there are 1 or 2 other families. I think it's a great option for kids who are young and/or quiet who don't enjoy the loud ruckus that comes with indoor play areas at malls and community centers.
When you walk in, the first things you see are a large train table, a tractor, and a giant LEGO model of Des Moines's only skyscraper (so far...), 801 Grand. You'll also find a play kitchen with toy food, a play ironing and clothes washing station, and an imprint table to make crayon rubbings.
To save their resources, they ask that each child only use 1 piece of paper for the crayon rubbings. If you think your child will enjoy the project, you might consider bringing a few pieces of computer paper with you.
Sometimes, we've stayed for lunch. Upstairs, there's a nice restaurant called Cafe Barattas that has an outdoor, rooftop patio. They're open from 11am-2pm on weekdays, and they have live music on Fridays. I took a video clip from one of our experiences there on a Friday afternoon. This was from May of 2016:
