"Einstein's Correspondence with His Children" contains many childlike and playful letters. Here are some excerpts.
A child named Tivoli wrote in a letter dated July 10, 1946: "Dear Sir... Our teacher said you were in America. I asked her if you were buried in America and not in England. She said you were not dead. My good friend Petto and I often discuss astronomy, which is our favorite extracurricular activity. Petto had a telescope that we used to watch the sky at night at school. We observe the Pleiades, Orion, Gemini, Mars and Saturn... We've been caught a few times, so it's been difficult..."
Einstein wrote back a month and a half later: "Dear Tivoli... I'm sorry to tell you that I'm still alive... I hope that in future the astronomical research of you and your friends will remain hidden from the eyes and ears of the university authorities. That is the attitude of most good citizens towards their government, and I think it is right." I wonder if Einstein could read between the lines to his little friend.
The 1951 letter, signed "Six Little Scientists," read: "Dear Professor... We were both in sixth grade and had been divided into two sides over an argument in class. There are six of us in one group and twenty-two of us plus a teacher are in the other. The question at issue is: if the sun went out and humans died out, would there still be life on Earth... We believe that even if the sun goes out, there will still be life on Earth. Please tell us what you think... I hope you will join us as six little scientists, so that we have six little scientists and one big scientist."
Einstein's reply: "Dear little friends: A few are sometimes right, but not you. If there were no sunlight, there would be: no wheat, no bread; There was no grass, no cattle, no meat, no milk, everything was frozen; There is no life." So Einstein also knew that everything grows by the sun.
A child named Carol wrote on November 12, 1952: "I am a sixth grader at West View School. We discuss animals and plants in science class. Some students don't understand why people belong to animals. I would be very grateful if you could write back and explain why man belongs to animals."
More than two months later Einstein wrote back: "Dear little friend: we should not ask, what is an animal? Instead, what do we call an animal? What we call an animal has certain characteristics: it takes nourishment, it is born to parents like it, it grows, it moves on its own, and when the time comes it dies. That's why we call insects, chickens, dogs, monkeys animals. What about humans? Think for yourselves in that way, and decide for yourselves whether it is natural to classify ourselves as animals."
The funniest was when a little girl named Ann wrote in childish handwriting: "Dear Mr. Einstein, I am a little girl of six. I saw your picture in the newspaper. I think you should get a haircut. There was no reply.
From these replies, we can see that Einstein had a childlike interest and, more importantly, a childlike heart. Einstein once taught arithmetic to a little girl in his neighborhood for a long time in return for sharing her candy. In high school, Einstein was obsessed with the "light chase experiment" -- what if he could go faster than light? This kind of curiosity is a kind of childlike innocence, he later became the first opportunity to establish the special theory of relativity.