Toddlers - Museum of Science and Industry

The Idea Factory on the lower level is the top spot for toddlers. It has lots of fun balls, water, blocks, and other things to play with. There is a separated area specifically for kids under 36 months, but once a toddler is walking comfortably they'll likely prefer the main Idea Factory the most. The rules that prohibit running and throwing balls are pretty hard to enforce with toddlers, but staff normally don't get too worked up about them. You'll need a free timed ticket to go in, you can get those by the entrance (you can choose any time that day, but there's a cap for each time slot so the tickets for immediate entry are often gone, you'll likely need to wait 10-60 minutes depending on how busy the day is). Although there are a few ways to play with water, most kids will stay dry if you roll up sleeves—still, it never hurts to have a backup set of clothes available.

Farm Tech, with a real tractor and combine kids can climb into, as well as a pretend cow to milk, is a great exhibit for kids this age. Flight on the top floor is a real Boeing 727 that kids will love to play in (and was helpful to explore and make my kids comfortable before their first flight).

The Great Train Story with model trains is very popular, although the trains are up high enough that you'll likely need to lift kids toddlers up to see. My kids always enjoyed picking a train and following it around the model. Look for a few interactive spots where you can push a button to start some action, from raising a bridge to explosives in a tunnel. Towards the back is an old-fashioned streetcar that kids can climb in and play with. The backs of the seats flip over which has entertained my kids for a long time.

Genetics is also a good spot for toddlers. The newborn chicks are fun to see, and there are a couple of mice in other parts of the exhibit.