Chicago, that toddling town

Does anyone know why Chicago is that toddling town? I know it's in the song lyrics but where did it come from? Thanks...

I thought maybe it was from the imagination of Fred Fisher, who wrote the song, but I took a walk at lunch, and by gosh, we all toddle.

Maybe from too many glasses of Johnnie Walker at lunch?

I always imagined it referred to Chicago being a new-ish city (i.e. toddling - toddler - young child)?