A large part of the protectiveness of children is about the fertility trend. Parents with four children think about safety very differently than parents with probably ever only one. I saw this on my home street growing up. The girl next door was an only child who her parents hovered over relentlessly. When I was ten, with three brothers, and told mom I was going exploring, she made sure I had a quarter to phone home if my bike got a flat and told me to have fun.

We joke about having a main child and an emergency backup child, but deep down it's not a joke, it changes our behavior.