An easy and safe way to view the sun (eg. during an eclipse)
Torch (if indoors)
Explain why that you should never look directly at the sun, not even with sunglasses, but that you can look at indirectly using various sorts of pinhole projector.
Get them to make simple pinhole projector using paper plates - make a pinhole in one plate using a drawing pin or compass: make sure the hole is not ragged.
Stand with the sun (or light source, if indoors) behind you: hold the plate without the hole in front of you at arms length, and the plate with the hole above your shoulder. Move the plate in front of you closer (or prop it up somewhere) to sharpen it or make it larger.
The further away the plate without the hole is held, the bigger the image of the sun.
If doing this indoors, switch the lights off and get them to try shining a torch through, to make the projected light smaller or larger.