Why do we stop running, spinning, jumping, singing out loud just for the joy of it? Why do we care if no one else is? Why should we care if people think we are bonkers? Just because we are grownups we are supposed to stop throwing our bodies on the ground and smelling the earth?
Some people say that people who don't have children are selfish. And your point is? Yes, I like the freedom to work and enjoy life with just little old me to think about. Besides, give me a break. Why do you think people have kids? To further the human race? For the kid's sake? Doubtful.
There's a theme of youthful indiscretion and testing one's limits, because what's charming at 20 is worrisome at 30, and alienating at 40.