There is a story that appears on social media every now and then about car seats for children that goes like this. When the most modern kind of car seats were made mandatory for children under a certain age (or weight) in the US, this saved lives: hundreds of lives, even. But it also made it significantly more expensive to have children. Not only were the individual seats quite pricey, but it became impossible to get three children into the back of an ordinary car. Having a third child required a family not just to get a new booster seat, but a new and much more expensive car. The effect of this measure on birth rates is measurable, and it seems that 70,000 American children have not been born as a result of it.