I have two children, ages 9 and 12. What are some fun things to do in Chicago with the kids when visiting this summer?

Besides baseball games - http://www.msichicago.org/index.html is where I am going when I go to Chicago.

The museum of science and industry is great for kids. Also the Natural history museum, acquarium w/ dolphin show and planetarium.

you can also rent bikes and ride along the lake, and take the architecture tour by boat.

I was in Chicago in Dec. 1999, and don't know if this stuff is still all there but here are my votes: Disney Quest, ESPN Zone, All-American Girl Doll Store, Jeckyl & Hydes Restaurant.

Disney Quest is closed. The children's museum on Navy Pier is good.

Field Museum: www.fieldmuseum.org. Museum of Science and Industry, as mentioned. Navy Pier, www.navypier.com -also home to a children's museum.
Boat tours are fun, and leave from the Michigan Ave. area. Check out the Chicago Tribune's site for more: www.chicagotribune.com or metromix.com

Also, American Girl Place, if you have daughters, is a great stop for tea - cute little sandwiches, get dressed up and bring your doll. John Hancock Center on Chestnut and Michigan. Shedd Aquarium has daily meet the animal events.

I was going to mention most of the things that others already have, but will add the Lincoln Park zoo. Also, if your kids (or you! ;-)) don't get freaked out by heights, go to the top of either the Sears Tower or John Hankcock building. Great views and I especially liked going at night. Enjoy Chicago in the summer - it's fantastic! I grew up near there, spent many days in the city, and miss it a lot.

We go to Chicago often with our daughter and granddaughter. We stay in the suburbs for inexpensive lodgings and take the train in - we're from small town so the train is fun - so is Union Station. We walk into downtown, the Sears Tower is good if the lines aren't too long. Always go to Navy Pier, granddaughter loves the fountain, which children play in, so we always bring a change of clothes. Children's museum at Navy Pier is for pretty young kids, but fun. So is the big ferris wheel. We like the Shedd Aquarium. FAO Swartze is fun, boys like the Nike store. It's busy but we enjoy the "Taste of Chicago" in late June, early July. People watching, shows, good food. Check metromix.com, there's a lot of good stuff there. Often there's a good play or show the kids will enjoy - we went to a Cirque du Soleil last summer that we all loved. Take the water taxi back to Union Station. Eat at Gino's or Giordano's for stuffed pizza.