is it near a train station? and how far from downtown??
Free is great but for those who haven't been to chicago before, i've heard the aquarium is worth the effort and it's not every city that has an aquarium like they do a zoo.
the aquarium and zoo, i think are gonna be good for smaller kids whereas MOSI might be better for those in school because of the learning experience...
whatever you want to do.. i'm willing to set up