You could spend a day discovering how a camera works (or your eye).
Maybe one day make a camera obscura out of boxes and trace the image -
Another day - use a variety of lenses, yardsticks and a flashlight to
look at the mechanics of a camera. Use a long table near a wall - the
yardsticks are tracks - have partners hold lenses along the track - turn
the flashlight on so the beam goes through the lenses and on the wall -
move the lenses - talk about what is happening to the light - depending
on how scientific you want to be they could keep a log - write
predictions and hypothesize -
How about reading a photograph - example you have taken - close up...
can they read the clues and tell what's happening in the setting - then
a photo that gives more information - how zooming in emphasizes -