Adult and child's gloves.
Magnets come in different shapes.
The learner will discover that magnets have a field that allows them to pick up or attract some metals through water, sand, and solids. The teacher will perform a magnet trick using a shallow box with nails in it. The teacher will secretly use a magnet under the box to make the nails move. Maybe the student will say that the glove is responsible so allow them to put on the child's glove and try again. They come in different shapes and sizes, but they all work the same.