Image Size ; One of the difficult concepts to get thru to a kid is the size of the image in a mirror. A plane mirror, like a bathroom mirror, will produce an image that is the SAME SIZE as the object no matter where the object is. To demo this, have a kid stand about 1 foot in front of a large plane mirror that is as close to VERTICAL as possible. With a hunk of soap or Crayola Washable Marker, have the kid draw a circle around his/her face so that the face is "framed". Now, have kid move backwards keeping his/her face in view at all times. Observation? No matter how far away he gets, his face appears framed and SIZED to the circle of soap. COOL!
Using ray diagrams, it is easy to show that a mirror must be a minimum of 1/2 the persons height in order to see the whole persons image. However, ray diagrams just aren't intuitive for the kids. This demo will help.