Reach into a bag of lollipops and remove a cherry lollipop. Cover it with a red silk and give it to a volunteer. Then drape a purple silk over a purple lollipop and hand it to a spectator.
Now, you tap the top of each lollipop still held by the volunteer and still covered with the same-colored silks and they magically change places! The red lollipop is now under the purple silk and the purple lollipop is under the red silk! Kids gasp when you uncover the lollipops they've been holding them the whole time!
If you like, they can keep the lollipops as souvenirs because you're completely clean at this point.
Great for kids, but it fools adults every time!