I rely on publications like TimeOut Chicago, emails from DailyCandy or an occasional RedEye to help me plan my weekends. But not everything featured is family-friendly or relevant to my visitors. This summer, when

Architecture boat tour and Navy Pier
The Chicago Architecture Foundation also has other walking tours.

Art Institute. Roofto

Other museums: MCA, Field, Shedd, Adler Planetarium
Green City Market (Wednesday and Saturday a.m. Out-of-doors during the spring/summer/fall)
Hancock Building Signature Lounge for a drink (I've never been to the restaurant, but I've heard it's nothing special. That's probably why

Sears' Tower (Aka Willis' Tower) for an amazing view! I first visited the Sky Deck when I was about five-years-old. I've never forgotten it.
Garfield Park Conservatory on far west side
Frank Lloyd Wright houses and tours
Street festivals
Movies in the Park in the summer (Check out the Chicago Park District. The schedule changes from year-to-year.)
Concerts in Millennium Park in the summer
Concerts @ Ravinia in the summer
Kayaking on the Chicago River. You could try this at another time of year, but I recommend summer.
Canoeing on the Chicago River