The Museum of Science and Industry is my favorite Chicago museum. They currently have a new Walt Disney exhibit that I look forward to visiting. Going to museums with a family can be pricey, but here are some Free Days for Chicago museums:
Adler Planetarium: free general admission with valid Illinois id on December: 2, 3, 4, 5, 9, 10, 11, 16, 17
Art Institute of Chicago: children 14 and under receive free admission always; Illinois residents get free admission Thursdays from 5-8pm
Chicago Children’s Museum: free admission for everyone Thursday evenings 5-8 pm, free admission for all ages under 15 the first Sunday of every month
Chicago History Museum: free admission for Illinois residents January 20th, with free special activities commemorating Martin Luther King, Jr. Day
DuSable Museum of African American History: free admission of Sundays noon to 5pm
Elmhurst Historical Museum: free; open Tuesday through Sunday 1pm to 5pm
Field Museum: free basic admission for Illinois residents on December 2, 5, 9, 10, 11
Fischer Farm: free; open to public Wednesday through Saturday 9am to 1pm
Museum of Contemporary Art: free admission on Tuesdays (open from 10am to 8pm) for Illinois residents
Museum of Science and Industry: December 9
Peggy Notebaert Nature Museum: Thursdays are free for Illinois residents (open from 9am to 5pm)
Shedd Aquarium: free general admission for Illinois residents on December 2, 9, 16, 23, 30
Also keep in mind that Chicago Public Libraries carry Kids Museum Passports, which allow entry into the museum for up to 4 people. http://www.chipublib.org/eventsprog/programs/kids/grkids_museumpass.php