We can all agree that children are the stupidest creatures on Earth. No contest.
At the core of this idiocy tends to be an inability to understand basic physics.
Things like gravity.
Or that a pendulum will continue moving until slowed by an outside force like friction or a kid's stupid head.
But sometimes it's not just ignorance about the laws of physics that dooms these moron babies; somtimes it's over-confidence in their understanding.