There's an ice skating rink in the new Millenium Park - it's artificial so should be there even with the relatively warm weather we've been having (0-5 C). You are most likely out of luck on any real snow.

If your son likes trains but you don't want to actually go anywhere, you can take the Brown Line elevated train which just circles the Loop. The website http://www.transitchicago.com will show where it runs. Some people fear the El because of the cross section of people, but I've taken my nieces and nephew on it all the time when they were young (still do - but they are all at least in their teens now) without any problem.

The Museum of Science and Industry has a big train display http://www.msichicago.org/ along with lots of hands-on type stuff - a walk-through heart, a submarine, a coal-mine, and also a plane - tho your son will probably be tired of planes after the flight here!

There is also the Lincoln Park Zoo - one of the few with always free admission and it's always open http://www.lpzoo.com/index_2.html

For other things to do - metromix is a good place to find out what's happening http://metromix.chicagotribune.com/

Marguerite in Chicagoland