Every summer I cover the inside of a shoe box with foil. The kids and I then make s'mores out in the sun. We talk about reflection, outside temp., solar power and such. We try it at different times of the day so the kids can get a feel for how the temperature rises and falls. Anyway, it's mostly just for fun now, but when they are older I will help them look up answers on the Internet.
Another sideways picture. Ahhhh, I swear it was fine 2 seconds ago.