If you need to build a prop magic mirror for a children's theatre production, or just an informal performance for children in your neighbourhood, you can make a simple prop mirror out of household materials. Orient the mirror prop so that the audience can see that the surface of the mirror is shiny, but cannot actually look into the mirror themselves. As long as the actors who address the mirror can speak to it convincingly, it does not matter that the mirror does not produce real images. Use a voice over effect by prerecording the mirror's lines or having an actor speak from off stage.
Draw a large oval with scalloped edges in pencil on a large piece of cardboard. Cut out along the pencil guidelines.
Spray paint the oval with gold spray paint. You only need to coat a section along the perimeter of the oval, which will be the mirror's frame, but spray paint more toward the centre of the oval as well to ensure that no unpainted cardboard will be seen.
Cut a large sheet of aluminium foil into an oval that is a little smaller than the cardboard oval. You may need to use several sheets to make an oval large enough to look right in its cardboard frame.
Glue the aluminium foil oval, or pieces of a larger oval, to the centre of the spray painted cardboard.
Decorate the frame with a black marker, making straight lines radiating out from the centre or wavy lines following the scalloped edges.
Mount the mirror prop by punching a hole at the top in the cardboard, stringing a piece of ribbon through the hole and making a loop, and hanging on a nail on the wall of the set.