Deutsches Museum

A brilliant hands-on museum of technology and science, the Deutsches Museum in Munich is a great place to take kids and interested adults. (Website http://www.deutsches-museum.de/index.php?id=1&L=1) There are lots of different galleries and well labelled (multi-lingual) exhibits. It's the largest science and technology museum in the world with over 1.5 million visitors a year. It's full of things to press and turn and will usually keep visitors entertained for a whole day or more.
You can see the first submarine in Germany, the first plane, the first car, the first computer, rockets, etc. etc., The aircraft extension site at Schleissheim (about 18km from Munich) has an interesting mix of German, Western and Soviet block aircraft and rocketry. The Theresienhoehe site holds most of the transportation exhibits (buses, trains, cars etc.) If you have any interest in science from physics, biology and chemistry to engineering, flight, micro-electronics and space travel. The museum is well worth a visit if you are lucky enough to be in the beautiful city of Munich.
If you can't make it to Munich the website will give you a good idea of what you are missing, but the photos don't have the same thrill as pressing the buttons and seeing the machines at first hand.