Taking apart a broken gadget like a fan or toaster is great for young minds and fingers. Kids get to unscrew things, learn how something is put together and have fun (cut off the cord for safety). If you don't happen to have anything broken lying around, you can buy small appliances cheaply at yard sales or thrift stores. Look for older versions. The newer appliances are mostly snap-together plastic.

Skip electronic devices, which might have potentially dangerous parts. Capacitors, for example, can hold voltage long after they're disconnected from a power source.