A great children's trick by Edwin, where two children can assist:

Hoppy is presented, printed in six colors on a 11.5 x 16.5 cm card. He is then placed in an envelope, which one of your helpers now holds.

You explain that Hoppy will jump from this envelope into another one, which your second assistant will hold. "Ready, steady..."
All the children shout: “...GO!”

But it obviously didn't work out as you said. The card remained in the envelope.
But when it is pulled out, everyone realizes that Hoppy has actually disappeared: the card has a hole the size of Hoppy's outline.

But where is Hoppy? After some back and forth, he finds himself on the back of one of your assistants. Laughter and applause!