Child B (picture 1): holds up a picture connected by ribbon to the Post-it Note showing the same picture. Child C (picture 2): holds up a picture connected by ribbon to the other Post-it Note.
Child D is another file on the computer. The browser (Child A) is looking for the two pictures (Child B and Child C) and can show them because they are where it expects them to be.
If picture 1 is moved (give Child B's picture to Child D), the computer still looks where it expects the picture to be (the ribbon is still held by B) - but there's nothing there for it to show (remove corresponding Post-it Note from Child A).
If the picture is put back where it should be (give Child D's picture back to Child B) then the browser can see it again (replace Post-it Note).
This also works well, with a few adaptations, to explain the mysteries of saving. ("Miss, the computer's lost my work again...") Teresa Wilson, upper primarylower secondary education student (ICT), University of Brighton