Children should be supervised or be old enough to understand the safety issues and handle these devices safely. Yes, actually - but in other ways, too. Perfectly straight, until something bends it. Change its direction by making it pass into another transparent material of different density, like glass or water. These depend on the wave nature of light, and are a little more difficult to explain.
Lenses bend light in useful ways.
Simple lenses can't form very sharp images, so lens designers or optical engineers figure out how to combine the simple types to make complex lenses that work better. This complex lens has 6 simple lens elements - click the small picture to see the whole camera. But you have to split it up to see this. You can't break up laser light into other colors. Lower-power laser systems can be used to send and pick up information.