Really need more info to truly be of help. Hotel budget? Interests? Food likes/dislikes?

As a starter, look into the Architectural bus tour downtown. Will take you round to all the major sights, get off/on at will. Can efficiently see all the major landmarks that way.

Take in a Cubs game for a wonderful slice of Americana.

Tour Frank Lloyd Wright's home/studio in Oak Park

If you have a car, take daughter to Gurnee Mills Outlet stores. Mag Mile is really nice, but expensive. She/you won't belive outlet pricing compared to home.

Make sure and try Chicago-style pizza & hot dogs.

Consider emancipating 21-yo. He could easily and cheaply stay at the Chicago Youth Hostel and meet other young folks. Depends on your tolerance for anxiety and his maturity.