Why did people in ancient times call the waiters in restaurants Xiao Er instead of Xiao San and Xiao Si?

Bartender refers to the waiters in ancient restaurants and hotels, also known as Xiao Er and Xiao Er Ge.

In the old society, ordinary people living at the bottom of society generally had no names. Only when you go to school can you have a scientific name, and once you become an official, you will have an official name. However, only a few ordinary people can go to school or be officials, and most people don't have this opportunity. So their names are mostly called by generations or the age of their parents. For example, Chang Yuchun's great-grandfather was called May 4th Movement, his second brother was called Liu Chong, his third brother was called Chongqi, and he himself was called Chongba. The waiters in ancient hotels or inns were obviously ordinary people, so people should also give them a digital symbol to address them. The boss in charge is, of course, the "shopkeeper", who knows two words, and those who can keep accounts are called "sir". These waiters are also called "shop assistants". Or; Xiao er'