What's the current exhibition again? They change them twice a year or so, but not all of them are any good. The soap bubbles one, for instance, was really, really dull.
If you're looking for a great museum to visit with kids, try the Verkehrzentrum of the
Deutsches Museum on Theresienhöhe. They are expanding this year, so try to go before they do and everyone thinks it's the coolest thing to do. They've got cars and bicycles and even an ancient steam engine, and everything is explained so well in such spacious and uncluttered surroundings that you'll find yourself spending much more time there than you'd planned. At my house we call it "Das Bobby-Car Museum" - they actually have a selection of bobby cars and tricycles for the kids to try out; there's also a spiral slide and some nifty computer games. It's a great place.