Are you driving or flying? There are plenty of farms along the route if you are driving. Same for making cheese.

For sure the University of Wisconsin in Madison could give you a tour of their dairy operation but its not really a farm. And I don't think they make cheese on campus, just ice cream. But there are some farms in the area that make their own cheese, would probably be your best bet to go to one of those. On my phone now so I can't look anything up but will later.

We are driving from St. Louis with another couple and their younger children. Any suggestions you might have would be great. My google searhes haven't been very fruitful.

Ok, here's a website with a list of a bunch of artisan cheesemakers in Wisconsin.

http://www.wisconsindairyartisan.com/artisans.html

Many of them are in southwestern Wisconsin, which would be a 1-2 hour sidetrip from I-39. I am assuming that you are driving up I-39 to Madison and then heading east to Milwaukee. That's probably the easier route rather than going through the Chicago suburbs to get to Milwaukee.

I'm going to link to a few that I think would be good for you (keep in mind I've no personal experience with any). I'm sure there are some closer to Milwaukee but southwest Wisconsin seems like more of the place for artisan cheeses. There are a bunch more on that link so feel free to browse if you want to stay close to Milwaukee - there are also goat and sheep cheesemakers on that list if you really want to see a wide range of options.

http://www.ottercreekorganicfarm.com/
Organic, pasture-based dairy farm that makes their own cheese. Located about 30-40 minutes west of Madison.

http://www.uplandscheese.com/index.html
Another smaller dairy that makes it own cheese. About an hour west of Madison.

http://www.edelweisscreamery.com/
Cheese factory only, about an hour from I-39, west of Janesville.