It might be interesting for your young son to learn that his testicles are sensitive to temperature. The testicles are located inside a sack of skin called the scrotum. The scrotum is very thin. It doesn’t provide good insulation from temperature changes that might affect the testicles. This anatomy illustration is from by book, “I’m a Boy, Special Me.”
Your son might have noticed that when he jumps into a cold swimming pool, his scrotum becomes wrinkled and moves closer to his body. This helps the testicles inside the scrotum to stay warm in the cold water.
The opposite happens when the scrotum becomes warm, like while he is wearing tight fighting pants or exercising. Since the temperature around the scrotum heats up, the scrotum becomes less wrinkled and hangs a little away from the body. This helps the temperature around the testicles to stay cool.
By teaching your son these small pieces of interesting information about his boy anatomy, he will feel more comfortable coming to you to learn more.