C., I live in Milwaukee, on the border of Brown Deer. It's not often we see that city come up on a national board!
What a great idea for your kids! I remember when I was a kid, my dad traveled quite a bit for work. He would always come back with a little something for "his girls" (my sister, mom & me). I looked forward to seeing what he got, & what the "story" was behind it. I still have some of the items even now.
For those of us in the area, Brown Deer isn't a stand-alone town, as much as it is a Milwaukee suburb, & almost a part of Milwaukee itself. Milwaukee is known for a few things - Beer, Brats & Brewers (baseball), Harley Davidson, Sprecher (beer & Root Beer). Wisconsin is further known for - Packers (football), Badgers (University football), cheese, hunting, more cheese.
The Milwaukee Brewers just recently adopted a "mascot", Hank the dog, and have been marketing items with Hank on them. That could work for both your kids (although might be expensive)
The Sprecher brewery is right off the freeway as you are traveling from Brown Deer to the Airport, you could stop in & get a 4-pack of Root Beer (or cream soda) to pack carefully, or even root-beer flavored popcorn! Much less expensive.
http://sprecherbrewery.com/soda.php
Cheese is always a good choice. The Wisconsin Cheese Mart in Milwaukee has a huge selection, including the wax-wrapped shaped cheese (Wisconsin, or cow), & is just blocks off the freeway downtown (also on the way to the airport)
https://www.wisconsincheesemart.com/cheese/shapes/
Hope this helps with ideas, enjoy your trip to our town! If you'd like any local info, feel free to message me. T. =-)