This came up when discussing the 'Pflegereform' in Germany. Everyone has to pay a proportion of their income and this tax is used to help pay for the cost of retirement homes for old people. The percentage of income you have to pay is slightly higher for people without children.
Usually this is justified by saying that people with children raise the next generation of people to pay for this but another argument is that children take care of their parents so the need or usage of retirement homes is smaller. I want to know whether the latter is true (in a statistical average sense).