A favourite with kids, (and adults who should know better) is this Electronic Voice Transformer which has 10 different hilarious changing effects. Just pull the trigger then talk, shout, sing or whistle into the microphone to amplify and distort your voice, it also features super-bright LEDs which only flash when sound is detected. 

• 10 Different Changing Effects
• Voice Activated LEDs
• Ages 3+
• 9V Battery Included