Second not driving downtown. Take the train in if you go. Check out Metra for the nearest station and schedules, but also look into the parking situation at the station before you go. It might be worth driving out to the Route 59 station, for instance, where there’s plenty of parking, as opposed to the Lisle station where there’s hardly any.
A lot depends on how busy you want to make the day. Get to the city in the morning and you can easily run yourself ragged by dinnertime. My standard recommendation is the Chicago Architecture Foundation’s river tour. Museum of Science & Industry, Field Museum, Art Institute, all great too. You won’t be able to do it all in one day.
If you want a more laid-back day, You may not need to go to Chicago proper at all. You’ll be staying very close to the Morton Arboretum and downtown Naperville, which has a number of good restaurants and shops.
Assuming you wind up in the city, I’ll recite my stock comment to grab lunch at the Signature Room lounge at the top of the Hancock building. No charge to enter and lunch with a drink will cost you less than the entrance fee for the Sears/Willis Tower. Dress is fairly casual and children/minors are admitted during the daytime hours (at night it becomes a more traditional bar and is dressier).
Agreed. If you’re staying where I expect you are, you’re probably less than five minutes from the Arboretum and about 10-15 from downtown Naperville. Naperville might be a good wind-down for dinner if you spend the whole day touring the city. Might not be too exciting for the young ladies, though.
Final update: We did the architectural foundation’s river cruise, which was fun even though it was raining. My daughters’ iPhones proved to be invaluable when trying to find the place. Got to get me one of those