"Some families defied the policy by having a second or third child. If the “population police” found out, they punished the parents by imposing fines that were well beyond most families’ ability to pay. Many such parents therefore kept their “above quota” children hidden from public view. Their official invisibility meant that these children were not given a residence permit, called a hukou, which meant they could not get health care, attend school, or even get a library card."