These photos were taken last October (when it was still warm) in Kansas City, MO.
My "three" boys were doing their all-time favorite hobby, railfanning. Ever heard of it? Me either. But apparently it is a huge past time for lots of people, most of them with the Y chromosome.
So, if you are ever in Kansas City, Union Station is an awesome place to fan some rails. Plus, it meets all 3 of my criteria for being "Toddler/Pre-Schooler Friendly" because it is
1) Free - at least the parts we visited
2) Has (relatively) clean bathrooms (also saw a "Mother's Room" for nursing moms)
3) the rail yard overpass is FENCED.
As a bonus, to get up to the overpass to watch trains, the boys love to ride on the "alligator", which would be the elevator to the rest of us.