Fun, educational, free...it's like the trifecta of the ideal family activity...and it's the Kalamazoo Valley Museum.   The museum has staple educational activities like those about the human body and how electricity is created as well as different exhibits that come in for a short period of time, things like the Magical School Bus (teaching about weather) and Dinosaurs (pretty self explanatory).  They also have a planetarium and occasionally show feature films concerning historical topics.  Check it all out at: http://kvm.kvcc.edu/.  And sign up for the newsletter so you can get all kinds of fun information to read with your kids at home.