My 30 month old son asked me why people's eyes will hurt if one stares at Mr Sun. I told him the sun shoots sunlight, which is not visible and not touchable. But it exists and is made of atoms just like other things we can see. If it hits our eyes, our eyes will hurt just like a man hurts from a car accident.
But it is not convincing answer, and I wonder if there is an easy way to explain this phenomenon to him?
I like the answer which discusses a sunburn.
To get a more visceral reaction, you could show him how a magnifying glass can burn things by "bunching up" (focusing) the sunlight. That should show him that the sunlight really is a destructive force.
My answer for a four year old girl:
"You know how your skin gets burnt in the sun? You know your eye is very soft? The inside is even softer and gets burnt very quickly. Pretty much straight away."
Tell him the truth, no weird contradictions. Mr Sun does not shoot something invisible, because obviously you can see light. Furthermore, it is not made of atoms (at least not in physical sense, of course, in some philosophical sense, it is).
Just mention that the Sun emits very very much light, and too much light hurts.
This is the way it is, although it answers his question by his premise. From a philosophical point of view, this is an answer he has to accept with no further explanations (like a dogma or an axiom).
This is the bare truth, not too much information, and every child is smart enough to cope with it.
The answer is not convincing because it is not true. Tell the child the truth: that we can see because our eyes are sensitive to light, like our body is sensitive to touch – and like too much touch (a hit, actually) may cut our skin or break our bone, too much light may burn our eyes' interior.
Atoms or EM radiation are irrelevant now, but it's important to emphasise 'too much light', because one can get too much light form other sources, too. For example one should avoid looking at naked bright light bulbs or into a torch light, and especially into laser pointers.
Take a bit of toilet paper, and hold it under the bath's faucet. Turn on the faucet just slightly, so there are small drips. See that? The paper holds.
Now turn the faucet on full blast. Does the paper hold up? Nope.
Intensity can be damaging/harmful. An example could be made by making a soft touch with one finger, or allowing a whole hand to fall two inches. Which is more intense and damaging? Likewise, you can make a powerful slap. (Slap your own skin... it won't be child abuse, it likely won't hurt, but it is likely to be loud.) Explain that intensity is damaging.
Explain that it is not just the sun that can damage eyes, but sufficiently bright light. Also explain that the sun is very intense light.
Explain that looking at the sun for two or three seconds is probably not going to be a major danger. But looking at it for longer can cause problems. Analogies can be touching something somewhat-hot, or some other stimulus that just gets annoying/painful/undesirable when sufficiently repeated.
Like other respondents, I think you should tell your son that the inside of your eyes can burn, just the same as your skin can, but quicker.
But because your skin is on the outside of your body, it has lots of pain sensors to detect when things could damage it. The inside of your eyes don't have pain sensors because they're inside your body where they don't get touched by damaging things. That means that when you damage your eyes, you won't feel it, which is why you need to be extra careful.
Use it as an opportunity to teach moderation.
Your child probably knows that being warm feels nice, but too much warmth can be uncomfortable, and even more can burn. A cool breeze is nice too, but too much and we get cold, and can even get hurt.
It's the same with light from the Sun, we like having enough so we can see, but too much and it can hurt us.
This can be used in similar lessons about other things that are nice in moderation, like candy, food, and a whole lot of other things they won't know about until adulthood.
Great methods are by showing it in a practical manner. Showing how a magnifying glass can harness the sun's power, or you can explain how everything we look at is reflecting light from the sun, and thus has been weakened in strength and doesn't hurt our eyes. But say you take a mirror which reflects almost all the light, that will hurt our eyes.
After you show these things, you can explain the seriousness of the matter, that our eyes are very sensitive to light so that we can see all this reflected light, but are way too sensitive for direct light, etc. And just as we get sunburned on our skin that acts as a shield, our eyes are not a shield and directly get damaged permanently.
Some other people said using it as an exercise of moderation. I agree with that totally and think that would be very effective.
Take a black piece of wood (or something similar, black metal will also do) outside with your son. Then stay for a short time in the sun. Let him touch the piece of wood (be careful if using metal, this can get too hot to touch). It should have gotten really warm. Now let your son look in a mirror and ask him what color his pupils have. Now he should have learnt that dark colored things will get very warm in the sun and this may be harmful.
point out to your son that the iris of the eye is a lens.
get a magnifying glass.
point out to your son that the magnifying glass is a lens.
take your son out on a sunny day.
use the magnifying glass to focus the sun light onto some flammable material like some paper.
State the obvious that the focal point in the back of the eye will react the same as the paper.
qed
You can give him a similar experience (though not actually damaging) by taking him in to a darkened room.
Wait in there a bit while your eyes adjust.
Then either turn the light on, or go out to a much brighter room.
The discomfort can illustrate your point without damage.
The sun is hot. Extremely hot. Hot things can burn. I don't believe you need to make the explanation any more complex than this, or attempt to explain it scientifically.
The answer you've given the child would likely confuse him more.
The analogy to a car accident I believe is not at all appropriate. The child presumably has no experience of car accidents, so would have no way to understand what a car accident would feel like. Speaking from experience, a car accident feels very different to looking at the sun.
If you're going to try to explain the concept of 'hurt'. It would be best to use something the child may have had experience with, grazed knees, ear infections, getting new teeth etc. The child would very likely understand that these are unpleasant sensations, so would want to avoid anything that may be equally unpleasant.
You could therefore say something like "if you look at the sun, your eyes may hurt, like your knee hurts when you fall down."
Also if you want the child to not look at the sun, avoid personalizing it. i.e. stop referring to it as "Mr Sun". The child might be trying to see Mr Sun's smiling face.
