It has to have been 20-ish years ago now (pre-smartphone/pocket internet), but I was traveling in Europe and my friends and we stayed in a hostel with a young woman from China.
We had a terribly hard time explaining the idea of "cousin." Once we did, she explained that she was unfamiliar with the concept because her family (and apparently all the families she knew well) had only had single children for generations.
I assumed there had to have been a word for it at some point, and that people were probably using it somewhere, but she seemed quite sincere in telling us she knew no such word.
The young woman in your anecdote is an extreme outlier. First, her family and all families she knew well only had a single child for generations; if that’s the case for most people, the population would shrink rapidly, so obviously most families aren’t like that. Secondly, to be unfamiliar with the concept at all, she had to be unfamiliar with some household names from cornerstones of Chinese literature, taught in grade school; very unlikely for a literate person. She also had to distance herself from television and the like, which was achievable twenty years ago.
Apologies for not using a better source than wikipedia, but I could believe that the anecdotal woman was not such an outlier, when you take into account that whole "one child policy" https://en.m.wikipedia.org/wiki/One-child_policy
That only started in 1979, with limited enforcement throughout, and gp’s talking about families with only one child for generations (probably >=3 in the context but at least 2) circa 2000 which is only one generation removed, so that’s only a small factor. Especially considering China’s population doubled from 1949 to 1979.
I also discussed the indirect/cultural factor where one should learn about this. There are two complementary factors here: if the young woman was rural there was practically no way she never encountered a family with multiple children; if she was urban it was more likely she was educated and thus should at least learn about it from school and/or through literature.
We had a terribly hard time explaining the idea of "cousin." Once we did, she explained that she was unfamiliar with the concept because her family (and apparently all the families she knew well) had only had single children for generations.
I assumed there had to have been a word for it at some point, and that people were probably using it somewhere, but she seemed quite sincere in telling us she knew no such word.