Everybody knows it, but it's not written down. This can be considered as a social contract. There are certain rules that are followed in society in which children must be respectful to those who are older. Being polite and saying "please" and "thank you" is just one rule. Another is the idea of calling someone by "Mr.", "Mrs.", or "Ms.". it is a common courtesy that must be followed. The extremeness to this social contract can depend on location, race, gender, and age. For example, in China, kids are taught to have extreme respect towards their elders. In America, kids are supposed to have respect, but it is not to the same depth.
The government must protect your natural rights. There are three natural rights: Life, liberty, property.